How can we add tax for our customers?

I'm facing this problem now. Do you already solved this??

Is your problem to add tax in customer?

My problem is that.. Upon payment of the supplier/customer , the account of withholding in COA should be updated. For example when we validate the invoice , account of Tax = 12 000 , but when payment is done account of tax would become 10 000 and withholding tax = 2 000