Exactly. Multiples of 5 are easy enough in my opinion, but the principle can be used for all kinds of stuff when trying to calculate quickly.

For instance 9x =10x-x is usually faster than 9x (at least for my brain).

I once talked to an old guy who called it "little math", because it fits in your head instead of having to use paper and pencil at the desk. It must have been taught differently before I was born. I work with numbers, and I've often encountered these old geezers who can eyeball a number close enough to make a decision before I can boot my pc and put everything through Excel.