B&H is now collecting tax for sales to customers in states that have post-Wayfair tax laws enacted, which is around 3/4 of the states.
Most of the states that have not yet done so will be doing so soon. California's goes into effect 2019-04-01, so those of you from California have until then to get your tax-free online shopping done.
Here's a page with the status for each state [2]. Here's another useful page [3] with per state info.
[1] https://en.wikipedia.org/wiki/South_Dakota_v._Wayfair,_Inc.
[2] https://taxcloud.net/topics/States%20News%20and%20Informatio...
[3] https://www.avalara.com/us/en/learn/nexus/find_your_nexus.ht...
In a few others they do not charge but they warn you that they report the sale to your state's tax authority, which could make it hard to avoid paying your state's use tax.