Amazon is actually supporting this legislation. There is a requirement for software to make this as easy as possible. Keep in mind it will only apply to companies doing 1 million or more in internet sales. Get ready for the proliferation of spin off companies that annually stop sales at 999,999 and refer you to their sister corporation that has exactly the same deal available. The proposed legislation also requires the state to provide free software to the merchant to assist in the proper collection of taxes owed.
Interesting side-point for what it is worth about Amazon. They may be about to increase by a large number the physical warehouses around the country. Up until now the sales tax was only collected in those states where they have a warehouse and they kept that uncommon to avoid taxes. If they want to be able to get purchases to you faster they need more nearby warehouses which means more of their sales will be locally taxed. Voila, as long as Amazon is going to have to do the tax collecting they might as well sign on for everyone else to have to do the same. Big money talks.
Here is the text of the proposal
Bill Text - 112th Congress (2011-2012) - THOMAS (Library of Congress)