Function to calculate GST

[Brian]

Hey guys,

Ive written a very simple function to check whether the GST that is calculated on a website is correct or not. The website displays the total value (cost including GST) and also the GST price seperately. Im just taking these values and inputting them into the following function -

Code:

Function Check_GST (theTotal, theGST)

standardGST = Get_GST(theTotal) [i](another function that i'm calling)[/i]
actual = theTotal - theGST
If (actual = standardGST )Then
    msgbox "this is tue"
else
    msgbox "this is NOT true"
End If    

End Function

Im calling this function from my script as -
Check_GST (total, GST)

but im getting the following syntax error message -
"Cannot use parentheses when calling a Sub"

Does anyone know why im getting this error and how i can rectify it?
Thanks,
Brian