Doesn’t the register tell you which bills and coins to hand back? Just punch in what the guy handed you lol.

Since 4 is less than 7, I subtract 10 from 54 to make it into (14-7)+(40-40). It’s basically what you do on paper.

I wonder if you’d get better mileage out of a high efficiency 12v brick, and a 5v and 3.3v DC-DC converter? Without changing your hardware out for a NUC or Raspberry Pi, I’m not sure if you can really go lower power. Maybe install a solar panel on your balcony for free electricity lol

Start attending local government meetings, it’s full of gossip and complex backstory.