Well, the title is a bit misleading. At least in California, people were always required to pay sales tax on the items purchased online. However, it wasn't until September of this year that Amazon was actually required to collect the sales tax and provide it to the government. After all, who would pay the tax otherwise?
Amazon will start collecting the sales tax by this time next year, meaning that Massachusetts shoppers can enjoy the sorta-tax-free shopping for another 11 months or so. Starting November 1, 2013, Amazon will start imposing a sales tax on purchases made by Massachusetts shoppers.
Over sites, such as Overstock.com, are not required to collect sales tax under this agreement, though it's only time before the state decides to try and squeeze more money out of the other sites. CNet reports that "Residents of New Jersey and Virginia will have to start paying up next year. Buyers from Tennessee, Indiana, Nevada, and South Carolina will also have to pony up sales tax sometime in the next few years."