1. A method for assigning taxability codes to purchases and processing tax invoices, said method comprising: determining, for a line item pertaining to purchase of a commodity or service for a user identified in a user profile to a first company group of a plurality of company groups, a first tax location and a first tax code of a plurality of tax codes, said determining the first tax location and the first tax code comprising using a process specific to the first company group that differs from another process that must be used if the first user were identified to a different company group of the plurality of company groups, each tax code denoting the line item as being taxable, being non-taxable, or having undetermined taxability; a computer generating a second tax code of the plurality of tax codes from the first tax code; ascertaining a tax jurisdiction from the tax location; after said generating the second tax code and said ascertaining the tax jurisdiction, said computer creating a requisition table comprising the second tax code, the tax location, and the tax jurisdiction; after said creating the requisition table, ascertaining for the line item a tax rate based on the second tax code and the tax location; after said ascertaining the tax rate, said computer generating a purchase order, said generating the purchase order comprising inserting the ascertained tax rate into the purchase order and transferring both the second tax code and the tax jurisdiction from the requisition table to the purchase order; transmitting the purchase order to a supplier of the line item; in response to said transmitting the purchase order to the supplier, receiving from the supplier an invoice specifying a payment due for the purchase order; and responding to the invoice by paying to the supplier a portion of the payment due or not paying to the supplier any portion of the payment due, said responding being in dependence on tax parameters comprising the second tax code and a tax indication of whether or not the payment due specified by the invoice includes a tax due to the tax jurisdiction for the line item.