Purchase Order with Tax Code and Tax Amount

Hi,

I have a requirement of having the vendor's tax code and calculated tax amount appeared in the purchase order.

I have found there is no place in the PO that I can enter tax code for the transaction. In the 'Manage Tax' button, I can only find the defaulted tax code from the tax rule to all POs which maybe incorrect for some vendors.

How can I create the PO with the correct tax code in it? Should I attached the tax code at the vendor site level and what other setup I need to do in order to have the PO picks up the vendor site tax code correctly?