it's state by state. i saw on reddit they said something like 22 states they have to charge sales tax in but the others they don't as of now. I don't get charged sales tax.
in the future, for folks who want to hit the minimum shipping threshold but may not see multiple items they want at once, you can order things to be in-store pickup individually, then once your orders get over $50, you can email plaidroom and ask them to combine and ship and they will not add a shipping charge. only downside is you definitely get hit with tax on those purchases.