In order to charge a sales tax, I believe that you have to have a tax certificate from the state in which you work. The sales tax that you collect is then paid to the state. If you are not charging a tax on your repairs I would say no, you shouldn't be charging tax on the materials that you use.
You may want to check with the state on charging and collecting sales tax on your business, it may save you alot of greif later on down the road.





