I would call my local SBA office to get information/contact information for tax questions in PA. NJ supplies tax bulletins that answer questions and list what items are tax exempt. BTW clothing is exempt in NJ but if you provide just the service of embroidery or screen printing that is taxable. Many NJ tax answers can be found at
http://www.state.nj.us/treasury/taxation/.
If you sell to a business that will charge tax to the end user you would not charge the business but should verify that they are a business that is subject to collecting tax and not an end user.