There is no tax on labor unless it is included in the total price without delineation. The logic is that if no one can determine the cost of labor from the invoice as presented then everything is taxed at the same rate. If you do work for a customer by installing material or equipment he provides then you don't charge any tax because he has already paid it upon purchase.
Charges for repairs in the home may not incur any tax deduction. However, one has to keep documentation to prove that no tangible personal property was joined to the repaired item. However, you can contact the local IRS offices for more inquiries.
It depends on what state you are in. Typically, Sales Tax is applied to both goods purchased and/or services provided, including labor charges. I know this is true for Ohio, Vermont, Maryland and Virginia.