Rounding numbers to the nearest 10 in Postgres

I have struggled with an equivalent issue. I needed to round number to the nearest multiple of 50. Gordon's suggestion here does not work.

My first attempt was SELECT round(120 / 50) * 50, which gives 100. However, SELECT round(130 / 50) * 50 gave 100. This is wrong; the nearest multiple is 150.

The trick is to divide using a float, e.g. SELECT round(130 / 50.0) * 50 is going to give 150.

Turns out that doing x/y, where x and y are integers, is equivalent to trunc(x/y). Where as float division correctly rounds to the nearest multiple.

If you want to round to the nearest 10, then use the built-in round() function:

select round(<whatever>, -1)

The second argument can be negative, with -1 for tens, -2 for hundreds, and so on.

To round to the nearest multiple of any number (range):

round(<value> / <range>) * <range>

“Nearest” means values exactly half way between range boundaries are rounded up.

This works for arbitrary ranges, you could round to the nearest 13 or 0.05 too if you wanted to:

round(64 / 10) * 10 —- 60
round(65 / 10) * 10 —- 70

round(19.49 / 13) * 13 -- 13
round(19.5 / 13) * 13 -- 26

round(.49 / .05) * .05 -- 0.5
round(.47 / .05) * .05 -- 0.45