Customizing AP_CUSTOM_WITHHOLDING_PKG to Round Off Withholding Tax

Hi,

I am trying to customize the seeded AP_CUSTOM_WITHHOLDING_PKG.AP_SPECIAL_ROUNDING to round off withholding tax.  It states on the Oracle Payables User Guide that the procedure is called during payment batch processing.  Problem is user wants me to automate tax rounding at the time of invoicing, not during payment.  Is there a way to do this using this package or another functionality?

Oracle Payables User Guide Release 11i:

"AP_SPECIAL_ROUNDING is called only when you automatically
withhold tax during payment batch processing. Modify this procedure
if you want to perform rounding of tax amounts during withholding.