Calculate Sales Tax based on work location

I run a repair service and we have to charge sales tax based on the location the work was done. The state gets a percentage, the county gets a percentage, and the city (if applicable) gets a percentage.

I have created the fields on the invoice content type to store the state, county, and city.

What is the best way to add percentage values to each of the counties and cities we work in and what is the best way to have the invoice automatically add up the percentages and charge the correct tax on the invoice?

Thank you!