How do I make an invoice program that calculates VAT?

A cashier program needs four things: a product list with prices, a fast sales screen that adds items and works out tax and totals, a printed receipt, and a report of the day's sales. You can buy a ready-made package, hire a developer, or describe what you want to an AI builder that builds it around your shop. Start with selling and receipts, then add stock and offers later.

Yes. Any Windows program can print through the printers set up in the system: a thermal receipt printer, an ordinary office printer or a label printer. The condition is that the printer's driver is installed and a test page prints from Windows itself. What remains is setting the paper size and receipt layout inside the program, and testing on your own device before you rely on it.

Take a copy of the program's data regularly and keep it somewhere other than the computer itself: an external drive, a second disk or cloud storage. A simple rule is one copy every working day and a weekly copy kept outside the shop. Most important, test a restore at least once, because a backup you have never restored cannot be trusted when you need it.