Texas shares a similar problem other states have as well. Based on somewhat unexpected population growth over last several decades, a single zip code no longer represents just one city. Many cities have, in fact, zip codes that represent the city and outside areas.

Susan Combs, Texas Comptroller of Public Accounts, included this quote in the October 2009 report on sales tax computation:

“Because many cities in Texas share a common ZIP code and many ZIP codes encompass an area both inside and outside a taxing jurisdiction, we do not recommend using them as a method of reporting local sales and use tax.”

To provide a workable solution, Texas has a Tax Rate Locator on its Web site, enabling users to enter a specific address to determine the taxing jurisdiction(s) at that address.

SpeedTax offers a similar, free service for real-time calculations that are mapped to any U.S. address, the SpeedTax Sales Tax Calculator. This service determines rates at the rooftop level, and splits out the total rate by taxing jurisdiction (state, county, municipality, special districts).