We charge tax on everything unless invoice is labor only. Do not know if it is correct nor is it my responsibility as it is not my business. I have seen invoices from other trades such as HVAC and electricians. Labor was not taxed. Watch for the different tax rate for counties. If you deliver and bill on site they must pay the local tax. Example. Flagler has a tax rate of 7% or still was as of recently. Do not know how they get the extra money. We were kindly reminded by the state. Not related to your question but thought it was good info to pass on.