It depends on what state you live in. Most states require you to collect sales tax for any sales that are made in your own state.
I would call a local CPA and ask them. I am sure they will answer your question over the phone for free. Always talk to a professional when dealing with tax and legal matters. Don't rely on advice from others here on the forum.
It all depends on many different things. some states are exempt, some arent, some items are exempt as well. Also depends on some if you have an actual physical presence or not.
Just talk to a tax pro about it. make sure its not just a HR-Block "Head" if it is just make sure they understand online commerce well.