More states are jumping on the bandwagon and requiring online merchants to collect sales tax even if they don't have a physical presence in the tax jurisdiction. Here are a few links to keep you in the loop...
10 states online sales tax laws go into effect today - Digital Commerce 360
Post-Wayfair Options for States - Tax Foundation
Economic nexus and future of sales tax - Avalara
It's certainly not straightforward and the requirements vary by state (even within states), so best to speak with a tax professional to help you navigate the changes.