Interchange allows taxing in a number of ways.
Simple salestax.asc table
The SalesTax directive is set to a form field or fields for user input, and those form fields are used look up the tax rate in salestax.asc.
Another simple tax method. A series of Interchange Variable settings are read to develop a salestax rate for one or a few localities, usually a state in the US.
Salestax multi -- VAT taxing
Levies -- multiple levels of tax