function round(out, a) {
  out[0] = Math.round(a[0])
  out[1] = Math.round(a[1])
  out[2] = Math.round(a[2])
  return out
}
Math.round the components of a vec3

@param {vec3} out the receiving vector
@param {vec3} a vector to round
@returns {vec3} out