function roundDigits (split, precision) {
  // create a clone
  const rounded = {
    sign: split.sign,
    coefficients: split.coefficients,
    exponent: split.exponent
  }
  const c = rounded.coefficients

  // prepend zeros if needed
  while (precision <= 0) {
    c.unshift(0)
    rounded.exponent++
    precision++
  }

  if (c.length > precision) {
    const removed = c.splice(precision, c.length - precision)

    if (removed[0] >= 5) {
      let i = precision - 1
      c[i]++
      while (c[i] === 10) {
        c.pop()
        if (i === 0) {
          c.unshift(0)
          rounded.exponent++
          i++
        }
        i--
        c[i]++
      }
    }
  }

  return rounded
}
Round the number of digits of a number *
@param {SplitValue} split       A value split with .splitNumber(value)
@param {number} precision  A positive integer
@return {SplitValue}
             Returns an object containing sign, coefficients, and exponent
             with rounded digits