I need to write a Function Procedure that will produce an amount displayed in a TaxLabel after calling it from my menu item calculate event.

Code:
Private Function TaxAmount(ByVal TaxAmountDecimal As Decimal) As Decimal
        'Declare variable for calculations.
        Dim OutputSubtotal_Decimal As Decimal
        'Determine tax amount.
        Return 0.08D * OutputSubtotal_Decimal
    End Function
Code:
Dim TaxDecimal As Decimal
        Dim AmountDue_Decimal As Decimal
        Dim CarSalesPrice_Decimal As Decimal
        Dim Accessories_Decimal As Decimal
        Dim OutputSubtotal_Decimal As Decimal
        Dim OutputTotal_Decimal As Decimal
        Dim TaxAmount_Decimal As Decimal
        Dim TradeInAllowance_Decimal As Decimal
Code:
OutputSubtotal_Decimal = CarSalesPrice_Decimal + Accessories_Decimal
                OutputTotal_Decimal = OutputSubtotal_Decimal + TaxDecimal
                AmountDue_Decimal = OutputTotal_Decimal - TradeInAllowance_Decimal
                TaxDecimal = OutputSubtotal_Decimal + TaxAmount_Decimal
Code:
AmountLabel.Text = AmountDue_Decimal.ToString("c2")
                AccessoriesLabel.Text = Accessories_Decimal.ToString
                OutputSubTotalLabel.Text = OutputSubtotal_Decimal.ToString
                TaxLabel.Text = TaxAmount(Decimal.Parse _
                                          (TradeInAllowanceTextBox.Text)).ToString
                OutputTotalLabel.Text = OutputTotal_Decimal.ToString
                TradeInAllowanceTextBox.Text = TradeInAllowance_Decimal.ToString
I'm only getting: $0.00 in the TaxLabel? After stepping thru the program, I found the error is in the, Function statement. After following several different examples, I'm still not getting the proper tax amount displayed?