Tracy,
Ian is correct that GP will allow you to set this up as well. I have found that Avalara, for what we do, is quite expensive. We manage all of our tax schedules our self (there are probably 150 or so).
You create a tax detail id for every tax "entity" (i.e. state tax, local tax, etc). You then match all those id's up to make a tax schedule.
So for example, we work in the Carolinas...for Pickens County I have a tax detail for SC (South Carolina) of 6% and a tax detail for Pickens of 1.5%. In the Tax Schedule ID, I create SC-Pickens and then move the SC and Pickens detail id's into that tax schedule. Now any customer who has a tax schedule id of SC-Pickens will be charge 7.5% (the sum of SC tax and Pickens tax) on all their orders.
You can get the tax rates for each county at the state's tax website.
Does this make sense?