How are you handling variable tax rates?

[MR <mtr...@du...>]

At the moment this is annoying but it may soon move up to a problem I'll
have to figure out how to solve.

We have a base state tax.  Then each county has its own tax rate.  
And sometimes the local city has their own tax rate.  The county/local
rates can be as low as 0% and as high at 1%

Right now, the tax rate is tied to the person entering the data.  
 
I can work around this by creating a custom inventory item for each  
state/county and adding that to every invoice.

Has anyone done a customization of the tables to place the tax 
rate to each customer, rather than to the ppl who enter the data?