There has been a rather widespread move throughout the country to define the "sales tax" as applying at the "point of delivery" or "point of use" rather than at the "point of sale." The primary purpose of this is to set in place the ability to collect "sales taxes" on internet purchases.
Of course, if the tax is a "point of use" tax, one must show a valid "address" (which usually is on your driver's license) and the tax must be collected accordingly. If the agent who sells you something does not collect the tax for the jurisdiction in which you live, of course as a loyal and honest citizen it is your responsibility to report to your local tax collection authority and pay the tax on any purchases you may have made elsewhere.
While there are serious ramifications in this, with respect to that Constitutional prohibition against any law in restraint of the free commerce between the states, undoubtedly greed will prevail, and it appears that it is not just in New York that this is happening.
Since the Indian excemption from local sales taxes rests on the status of the tribes as "sovereign nations," collection of this tax amounts to the application of an "import duty" by the state - something that has been held illegal in past actions in Federal courts, but undoubtedly greed again will prevail.
This is NOT a Federal mandate so far as I've heard, and it seems unlikely that the Federal government would have a part in it. There are NO Federal sales taxes on any domestic sales. It is a State "money grab." It is more likely that New York asked the Fed to make the Indians collect it for them, since the state has no authority to make the Indians collect it. The Fed most likely said "ain't our problem, you'll have to do it yourself."