Where I live, if I call a plumber, I pay his bill, and federal and provincial taxes. Ditto for painter, electrician, I have to pay sales taxes. So what is the difference if the programmer works to build a website. Do you pay his invoice without paying sales taxes?
Sales tax is payable on goods, not services. Building a website is a service. You don't pay sales tax when you procure the services of a doctor or lawyer; why would web coders be any different?