Tax Configuration

There are not enough conditions for charging taxes and I need to know how to modify this feature.

My client wants to charge state tax ONLY if the billing and shipping address are within the state that she lives.

Within tax set up, I can see that I can set taxes to apply based on shipping address OR billing address. How do I apply a condition that says:

If shipping address AND billing address are in Colorado, then charge 2.9% state tax


Apparently, this tax configuration is required by many states in the USA. The law is targeted at internet businesses.

Does anyone here kjnow how to setup taxes in CS-Cart allowing both the shipping & billing address to govern the application of taxes.