in the US, I pay sales tax to the people who do repair work on my house and who fix my dad's computer, and for the software I get from Apple engineers, all of which are not taxed within a firm.
I have always interpreted http://apps.leg.wa.gov/wac/default.aspx?cite=458-20-155 regarding computer repair as the idea that if I am replacing a piece of faulty hardware that I must charge sales tax for the attached service, but if I am merely cleaning off viruses, that this is a professional service and therefore not subject to sales tax. I have not been able to find a clear authority for this however, and it isn't clear as to whether hooking up and configuring an external modem that the customer bought from someone else is taxable.
Repair however is a problematic term. A lawyer might be involved in sending a letter threatening action of a problem is not repaired but that service is not taxable itself.
In Washington State, professional services not directly tied to an improvement of tangible property are not generally taxable. So landsacping and lawn care is generally taxable, but open source software development is not (since it is not a sale of a license, or a one-of-a-kind development aimed at one customer only).
http://dor.wa.gov/content/findtaxesandrates/retailsalestax/
"Similarly, when a business purchases a retailing service for its own use, it must pay sales tax on the purchase." "