roundToStep.ts

function roundToStep(n: number, step: number) {
  n = Math.round(n / step) * step

  // Determine the number of decimals to round.
  let p = 0
  if (n % 1) {
    const s = String(n)
    p = s.length - s.indexOf('.') - 1
  }

  if (p) {
    const q = Math.pow(10, p)
    return Math.round(q * n + q / 1e16) / q
  }
  return n
}