Cash is great, cash is the new gold. Before they were printing money, last millennium. This millennium, they just shift numbers to the left, on a computer. It's all numbers in your app. This is currently considered better, but is much worse.
$20 at most, bigger denominations aren't worth much. I wouldn't accept $100 as payment without someone to verify it, or going together to a bank to deposit it. And like the bills have to be in pristine condition, always complain if someone is trying to give you a damaged bill, that limits its spendability. Gotta know the bills well, maybe ask your bank if they can let you see for yourself the difference between real and fake bills so you can tell the difference. Banks can always get fresh bills by turning in your old ones, to keep up their condition. Plus newer bills have better copy-protection, and are therefore easier to verify.
And guess what? Your purchases will generally not be traced if you pay cash. This is important for books, stationary, electronics, medicine, and charity.