Adding totals from CheckBox Controls and display in labels

[RodPhp5]

I need help on this im stuck...

I am supposed to add price of the selected accessories and exterior finish if they have been checked, and display the result in Subtotal. Calculate sales tax on subtotal and display the result in Total label, and finally subract the trade-in allowance from the Total label to get Amount due. I have developed the code but my problem is that when i check the checkboxes the totals are not displayed, but if i dont check the checkboxes the totals are displayed.

Private Sub CalcButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CalcButton.Click
        'declaring local variables
        Dim sngBasePrice, sngAllowancePrice, msngSubTotal, sngSalesTax, _
        sngTotalPrice, sngGrandTotal As Single
        Dim sngStereo, sngLeather, sngNavigation, sngStandard, sngPearlized, _
        sngCustomized, sngTaxRate As Single
        sngStereo = 425.76
        sngLeather = 987.41
        sngNavigation = 1741.23
        sngPearlized = 345.72
        sngCustomized = 599.99
        sngTaxRate = 0.08
        'assigning values to variables
        sngBasePrice = Val(Me.BasePriceTextBox.Text)
        sngAllowancePrice = Val(Me.TradeInAllowanceTextBox.Text)
        'checking which TexBox was clicked, and adding neccesary amount
        Select Case True
            Case Me.StereoCheckBox.Checked
                msngSubTotal = sngStereo + sngBasePrice
            Case Me.LeatherCheckBox.Checked
                msngSubTotal = sngLeather + sngBasePrice
            Case Me.NavigationCheckBox.Checked
                msngSubTotal = sngNavigation + sngBasePrice
            Case Me.StandardCheckBox.Checked
                msngSubTotal = sngStandard + sngBasePrice
            Case Me.PearlizedCheckBox.Checked
                msngSubTotal = sngPearlized + sngBasePrice
            Case Me.CustomizedCheckBox.Checked
                msngSubTotal = sngCustomized + sngBasePrice
            Case Else 'calculations
                msngSubTotal = sngBasePrice
                sngSalesTax = msngSubTotal * sngTaxRate
                sngTotalPrice = msngSubTotal + sngSalesTax
                sngGrandTotal = sngTotalPrice - sngAllowancePrice
                'display the total amounts in label controls
                Me.SubTotalLabel.Text = msngSubTotal
                Me.TotalPriceLabel.Text = sngSalesTax
                Me.AmountDueLabe.Text = sngGrandTotal
        End Select
    End Sub
End Class