New York DOES require you to pay sales tax on items purchased out of state and there is a line on your income for it, however it is widely ignore
Most ecommece occurs on larger sites like eBay, Amazon, Wal-mart etc. those sites can collect the sales tax instead of the merchants who sell on them and that would collect the majority of the sales tax owed (B&H sells on eBay and Amazon so sales on those sites would be subject to sales tax collection, but sales on their own site would be harder to collect