Tax in Purchase Order : Tax Rate from Tax Jurisdiction code/Tax Code

Hi,

As I understand for US and Canada, tax is calculated from Tax Jurisdiction code. How ever, there are tax codes in system, which have the tax rates in FTXP. From there the tax rate is picked, when we enter the tax code in the PO item, in invoice tab. I wanted to know,

1. what is the role of Tax Jurisdiction Code here.

2. Is the tax code and the tax jurisdiction code linked?

Regards

SR