I agree with Janice. It's a megacorporation welfare plan that will screw small businesses; now, if you order on-line from out of state (And the business doesn't have a physical presence in your state), you pay price plus shipping. If you buy locally, you pay price plus tax. It's pretty much a wash for the buyer. This is huge overhead burden for truly small businesses that would have to deal with literally thousands of different tax rates.
There are several approaches that would make this less onerous, if it has to be at all. It could simply impose the tax at the sending state end (Which is similar to how in-state internet sales are taxed in most states now, the business pays the rate applicable to its own location, not the rate applicable at the receiving end, which within my State could be anywhere from about 4.5 % to over 8%), which would be simple and not require an army of accountants. Or, each participating state could be required to have a single tax rate for out-of-state internet sales. Or, for that matter, it could be made to apply to businesses that only do a large dollar value of internet business, such as a million dollars in gross internet sales per year.
Any State that even has a sales tax would be nuts to opt out of this as it stands, since that State's own population isn't benefited by the State standing out of it, they already have to pay sales tax on in-state sales and the people there would now be paying taxes to 49 other States but nothing extra coming in, a variety of the "Spanish prisoner" dilemma so popular in psych experiments, as taxpayers being forced to pay taxes through another state strike back by returning the favor.
It won't produce nearly as much revenue as is being touted for it, and it will put another barrier in front of truly-small and start-up businesses, losing them the one tiny advantage over pervasive megacorporations in overhead costs that they presently enjoy.