Thursday’s item on that proposed “Internet sales tax” drew a sharp response from Mark Alger, who declared it wholly unconstitutional based on a passage from Article I, Section 9 of the Constitution: “No tax or duty shall be laid on articles exported from any state.”
Congress does not have the authority to permit the states to collect sales taxes on goods traveling between states. Note that the actual text of the Constitution refers solely to the goods themselves and make no mention of the location of the businesses or individuals shipping or receiving. Only that the goods be carried out (that’s what “export” means to carry out) of one state.
It might be argued that states may collect taxes on goods imported to the several states, except that only Congress has that power, and may not delegate it, and, at least for commerce within the United States, any good imported to one state must first be exported from another, and the taxation of that transaction is forbidden by the above provision.
Bottom line: You can’t enact this scheme without actually amending the Constitution. Then again, relatively few members of Congress pay anything more than lip service to the Constitution, and then only when they need it to support their own positions.