Hi,
If you want to check amounts of withholding tax for the vendors, you have some options to view it. You can access the WITH_ITEM, LFC1 tables by SE16. You have too the S_P00_07000134 report. This report is developed for the Colombia but I already used for the another country with the ABAP development for this country.
Also you can use table join BSIK and WITH_ITEM by SQVI for the open items and BSAK and WITH_ITEM for cleared items. It is more simple and fast.
JPA