Please share any logic to round withholding tax in ap_custom_withholding_pkg

Please share any logic to round withholding tax for Amount and Base Amount in ap_custom_withholding_pkg

Currently I was using below logic in ap_custom_withholding_pkg. But it was showing Error in some Invoices of Prepayment Application and some times wrong Tax Calculation on Prepayment Application Invoices

--bug13334982

AP_CUSTOM_WITHHOLDING_HOOK_PKG.Ap_Special_Withheld_Amt

                                     (P_Withheld_Amount

                ,P_Base_WT_amount

                ,P_CurrCode

                ,P_BaseCurrCode

                ,P_Invoice_exchange_rate

                ,P_Tax_Name

                ,P_Calling_sequence

                ,P_Unrounded_WT_Amount

                ,P_Calling_parameter

                                      );

--------custom Code begins from here----------------

--Logic:(Round down to precision zero)

     if nvl(P_Calling_parameter,'') ='HEADER' then