Not sure how charging for purchases under $5 contributes much to money laundering
Because it allows you to insist that yes, absolutely, the bulk of the business is cash-only. Rather like gaming machines, tanning salons, taxis, ice-cream vans, and pop-up car washes, you can then insist that you had a really good day's trading, and all that money in the till came from legitimate customers, honest.
Pay your tax on the earnings, tah-dah, clean money.
No, it's not going to give you Trump-like levels of money laundering (oh noes, I has made a massive loss in my casinos, how could this possibly happen), but for regional-level criminals?