The District of Columbia sales tax rate is currently 6%. No other municipality can add local sales taxes on top of the state rate.
Taxes in the District of Columbia are destination-based, meaning the District of Columbia sales tax rate is based, or determined from, the shipping address. This complicates business for retailers who need to have the exact and up-to-date sales tax rate for every shipment they make.
Follow this link to the District of Columbia Department of Revenue for more information.