The Sales Tax API provides rates in three levels of granularity based on your subscription.
The 5-digit ZIP code level will return all jurisdictions related to a single ZIP. There could be more than one result for a single 5-digit ZIP so all will be listed in your result.
The SalesTax+4® level will narrow down the jurisdiction based on the 9-digit ZIP code.
The Spot-On® doorstep-level will pinpoint the jurisdiction by geolocating the full street address.