Sales Tax

Wether a company owes collects a sales tax is dependent on wether that company has a "presence" in the district.  If the company does have a presence, then it must pay the tax.  Otherwise, the buyer is responsible for paying, though very unlikely to do so.

Often it also owes a sales tax to the city as well (Chicago and New York for instance).  Sometimes it owes a sales tax to the county as well (Cook County, IL for instance).

Some locals put different tax rates of special items, like food and clothes. There is no universal database of sales taxes owed by address.

Internet companies have not been offering tax payments to local governments, in violation of the local laws.

Congress has just passed a law that prohibits states from putting taxes on internet commerce.  But before this, the practice was both common and illegal.