A system and method for assigning taxability codes to purchases, and processing tax invoices, by company groups. A user, identified to one of a group of companies, inputs a requisition. Tax code and tax location are identified in a front end process applicable to the object of the requisition and converted into a converted tax code and tax jurisdiction and fed to a back end processor. Responsive to converted tax code and the tax jurisdiction for the corresponding company group, the back end prepares a purchase order which is transmitted to a supplier. Responsive to an invoice from the supplier and company group and tax code indicia from the purchase order, the back end processes and selectively pays, short pays, or rejects the invoice.