Regression Testing

Regression Testing
Common methods of regression testing include re-running previously run tests and checking whether previously fixed faults have re-emerged. Although this may be done through manual testing procedures using programming techniques, it is often done using automated testing tools. Such a 'test suite' contains software tools that allow the testing environment to execute all the regression test cases automatically; some projects even set up automated systems to automatically re-run all regression tests at specified intervals and report any regressions.
Types of regression
Local - changes introduce new bugs.
Unmasked - changes unmask previously existing bugs.
Remote - Changing one part breaks another part of the program. For example, Module A writes to a database. Module B reads from the database. If changes to what Module A writes to the database break Module B, it is remote regression.
There's another way to classify regression.
New feature regression - changes to code that is new to release 1.1 break other code that is new to release 1.1.
Existing feature regression - changes to code that is new to release 1.1 break code that existed in release 1.0.

Tax Determination- A doubt

For a material costing $120 gross price, discount is $20, thus net price is $100.
Now for some some states tax is calculated on the net price i.e. $100 , and for some some states it is on gross i.e 120$. How would this configuration be done.

We can use two tax codes to pick different tax percentage value, but how do we configure on what base price the tax percent is applied i.e. on net or on gross.