DOTS FastTax (referred to as FastTax or FT) is a publicly available XML and JSON web service that provides sales tax rate information for all US areas based on several different inputs. The service provides zip, city, county, county fips codes, state, tax rates and exemptions. 

FastTax can provide instant sales tax rates for any address, zip code, city or county in the United States.

Developer Guide

Integration Basics

NOTE: For rates in Minnesota, please use GetBestMatch.  Minnesota tracks tax rates differently from the rest of the states (they have zip code level rates).  Getting rates based on zip or city and county lookup operations will not necessarily return accurate results.