> Businesses don't do this. Unless they're money laundering fronts, businesses don't buy stuff in actual physical cash unless they have to, and they know that any cash discount would be from under-reporting the sales tax and that recording the transaction would be bad for both sides.
There's nothing wrong with buying computer parts with cash for your business and then writing it off. I do it whenever I'm in a pinch and want something "right now" instead of ordering it online and waiting for shipping. A store will give you a receipt.
I choose to use cash whenever possible to purchase small and large things because I don't like the idea of banks and other payment providers profiting from me without sharing those profits.
Unfortunately my business involves accepting money digitally, but I say it's unfortunate not because I'm trying to cheat any systems. It's because I'm forced to allow banks and other entities to harvest my private financial data and leverage my money for profit, and the alternative of not doing that is worse (ie., I personally accept it instead of being unemployed and homeless).