Forum Moderators: buckworks
As for a prospective tax, that's another matter. And if for some reason you collected such a sales tax in the past but failed to pass it along, that's also another matter.
The big thing is NEXUS. If you don't have a presence in a particular state (the state can't require you to collect the sales tax).
The definition of NEXUS is complicated, and is differnt from state to state. For example in Florida, if you have a company drop ship for you from Florida, it is considered NEXUS and you are required to collect sales taxes from Florida residents. In other states, a physical presence is needed for NEXUS.
The states are working on a project to have a uniform sales tax, and require merchants to collect sales tax from all states on Internet sales. Getting the required 35 states to agree on anything is next to impossible, so this process is going very slowly and wont happen for another 2 years, and most likely never.