What I need is EXTREMELY basic code to make these checkboxes add .25 cents for each one that is clicked. I tried this:

If chkBox1.Checked = True Then
txtTextBox1.Text = txtTextBox1.Text + 0.25
End If

If chkBox2.Checked = True Then
txtTextbox1.Text = txtTextbox1.Text + 0.25
End If

etc... and it seems to add incorrectly, .25 at first, then .75, then it goes up by .75 intrevals. Also, it adds every single time a checkbox is clicked on or off, I need it to take off the .25 cents if it's unclicked. It has 4 checkboxes, please help!! Thanks