Math like this will probably be a bad thing if you are aiming a missile to hit a target thousands of miles away but for ordinary life, i think it’s quite fine. I use 1610 meters a mile, because it’s easier to round up — a half mile then becomes 805 meters, a quarter mile 402.5 miles, a tenth of a mile is 161 meters. If you rounded down to 1609 meters, that math becomes a lot harder to do in your head.