R12 How to apply tax zone for managing us sales tax?

 Hi friends,

For US location based sales tax, we can set state level, county level, city level tax regime. But for some states, even there are different counties, some counties are sharing the same tax rate. So instead set up the same tax rate for each county, city, we can use tax zone to manage the counties that are sharing the same tax rate. However, when I set up tax regime as tax zone and finish all the ralated tax set ups, in ar transaction, the tax is not automactic calculated. When I set the tax regime as state/ county level ,