If you produce an accounting application, keep in mind that tax systems are different in many countries. In the EU, for example, a gross tax is named a value-added tax. There is no local sales tax.
BTW since July 2003 you have to collect European VAT ids from customers, if you ship software to EU countries, or charge them the vat of the EU country you are registered in. An analog tax collecting system will be established in other countries, so be prepared.
This is pure logic, and UI design. So when you code accounting application you will agree with us: That is up to you.