Labels changing depending on value in other labels

I am creating a POS system and on the subtotal page I have various labels such as 'cash', 'card', 'voucher' etc. Say for example a customers total comes to £20 and they want to pay £10 of it in cash and the other £10 with their card, I am having problems getting the labels to total up as they should. The 'total tendered' label displays 0.000 even though it should say £20.00 and the balance and change labels always display 0.00 even if they should say other. I know this is very basic but I have tried to figure this other for ages now and im getting nowhere. I have also tried calling values in from the database but have had no joy with that either. Thanks.
(I only included one payment button click event as they are all the same except for the labels name changing e.g. lblcash.text would say lblcard.text in the card click event.)

Code:

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Private Sub btnCash_Click(sender As Object, e As EventArgs) Handles btnCash.Click

        'Payment methods...........??
        '2 cash entries
        'cash and card
        'gift voucher and cash
        'gift voucher and card

        'HAVING PROBLEMS GETTING CARD AND GIFT VOUCHERS TOGETHER WITH OTHER METHODS

        If txtCash.Text = "" Then
            MessageBox.Show("Please enter amount")
        ElseIf txtCash.Text >= "0.00" Then

            lblCash.Text = txtCash.Text
            lblCash.Text = FormatCurrency(lblCash.Text, 2)

            lblTotTend.Text = (lblCash.Text) + (lblCredit.Text) + (lblVoucher.Text) + (lblOther.Text)
            lblTotTend.Text = FormatCurrency(lblTotTend.Text, 2)

            'DISPLAYING AS £0.00
            lblBALANCE.Text = (lblTOTALDUE.Text) - (lblTotTend.Text)
            lblBALANCE.Text = FormatCurrency(lblBALANCE.Text, 2)

            If lblBALANCE.Text < "0.00" Then
                lblBALANCE.Text = "£0.00"
            End If

            lblChange.Text = (lblTotTend.Text) - (lblTOTALDUE.Text)
            lblChange.Text = FormatCurrency(lblChange.Text, 2)

            If lblChange.Text <= "£0.00" Then
                lblChange.Text = "£0.00"
            End If

            txtCash.Text = ""

            SqlStr = "UPDATE Subtotal SET CASH = '" & lblCash.Text & "'"
            With CMD
                .Connection = CN
                .CommandType = CommandType.Text
                .CommandText = SqlStr
            End With
            DataP = CMD.ExecuteScalar

            SqlStr = "UPDATE Subtotal SET CHANGE = '" & lblChange.Text & "'"
            With CMD
                .Connection = CN
                .CommandType = CommandType.Text
                .CommandText = SqlStr
            End With
            DataP = CMD.ExecuteScalar

            SqlStr = "UPDATE Subtotal SET BalanceRemain = '" & lblBALANCE.Text & "'"
            With CMD
                .Connection = CN
                .CommandType = CommandType.Text
                .CommandText = SqlStr
            End With
            DataP = CMD.ExecuteScalar

            SqlStr = "UPDATE Subtotal SET TotalTendered = '" & lblTotTend.Text & "'"
            With CMD
                .Connection = CN
                .CommandType = CommandType.Text
                .CommandText = SqlStr
            End With
            DataP = CMD.ExecuteScalar
        End If

        SqlStr = "INSERT INTO SalesLog(ReceiptID) SELECT Id FROM Subtotal"
        With CMD
            .Connection = CN
            .CommandType = CommandType.Text
            .CommandText = SqlStr
        End With
        DataP = CMD.ExecuteNonQuery

        SqlStr = "INSERT INTO TransactionLog(ReceiptID) SELECT Id FROM Subtotal"
        With CMD
            .Connection = CN
            .CommandType = CommandType.Text
            .CommandText = SqlStr
        End With
        DataP = CMD.ExecuteNonQuery

        ' Added this statement to try solve problem with totaltendered label
        SqlStr = "SELECT SUM(TotalTendered) FROM Subtotal"
        With CMD
            .Connection = CN
            .CommandType = CommandType.Text
            .CommandText = SqlStr
        End With
        lblTotTend.Text = CMD.ExecuteScalar
        lblTotTend.Text = FormatCurrency(lblTotTend.Text, 2)

        'UPDATES THE PRICE LABEL TEXTBOX WITH THE LATEST PRICE TOTAL WITHIN THE ACTIVE TABLE!!
        SqlStr = Nothing
        SqlStr = "SELECT SUM(Price) FROM Active"
        With CMD
            .Connection = CN
            .CommandType = CommandType.Text
            .CommandText = SqlStr
        End With
        lblTOTALDUE.Text = CMD.ExecuteScalar
        ' lblTOTALDUE.Text = FormatCurrency(lblTOTALDUE.Text, 2)

        If lblBALANCE.Text = "£0.00" Then
            Reset()
            Application.DoEvents()
            'TILL DRAWER OPEN
            Threading.Thread.Sleep(5000)
            Me.Close()
            Login.Show()
        End If

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Your Problem:
You are calculation with TEXT!
For example:

Code:

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lblTotTend.Text = (lblCash.Text) + (lblCredit.Text) + (lblVoucher.Text) + (lblOther.Text)

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All the .Text properties are holding STRINGS. Even if you format that String to a currency-format it will remain a string.
In order to do correct calculations you need the parse those strings into numeric variables, do the calculations on them and then display the resultion number in a label or textbox using to .To String Method!

Yeah but I obviously got mistaken as the values in the labels are all numeric.