The standard-ish way to round to the nearest multiple in javascript is a function like this:

const round = (number, step) => {
  return Math.round(number / step) * step;
};

This works great. There’s absolutely no need to modify it and you should probably just stop reading here. But there’s another neat method that uses the modulus operator.

const round = (number, step) => {
  const half = step / 2;
  return number + half - ((number + half) % step);
};

The problem with this method is that it doesn’t handle negative numbers correctly. You’ll get round(-1,1) === 0 when it should be -1.

You can fix it by inverting the step when dealing with negative numbers:

const round = (number, step) => {
  if (number < 0) step = step * -1;
  const half = step / 2;
  return number + half - ((number + half) % step);
};

There are reports this method is quite a bit faster in javascript, but my tests have shown inconclusive results, so probably don’t bother changing anything.