1. sumdollaramtDecimal has to be more than 0 for any sum to be added to it. This looks like a logic error. Should that be If dollaramtDecimal > 0 Then sumdollaramtDecimal += dollaramtDecimal?
2. You need a process to transfer the text from the text box to the numbers you are using to track the order. That isn't shown. Are you sure that dollaramtDecimal has the calculations loaded before you cleared the boxes? Something like
if IsNumeric(quantityTextBox.Text) and IsNumeric(dollaramtTextBox.Text) Then
Dim i int32
i = quantityTextBox.Text
dollaramtDecimal = dollaramtTextBox.Text
dollaramtDecimal *= i
End If