Hi
Also make sure you maintain the rounding rules as 100 in the below path:
Financial Accounting (New) >> Financial Accounting Global Settings (New) >> Withholding Tax >> Extended Withholding Tax >> Calculation >> Withholding Tax Type>>Define Rounding Rule for Withholding Tax Type
This needs to be maintained for the company code and with holding tax type you are using.
Regards
Sanil Bhandari