public function round($decimals = 2) {

		if(false === ('-' . intval($decimals) == '-' . $decimals)) {
			return trigger_error(sprintf('Argument 1 passed to %s() must be of the type integer, "%s" given', __METHOD__, gettype($decimals)), E_USER_ERROR);
		}

		return $this -> convert(function($number, $decimals) {
			return round($number, $decimals);
		}, [$decimals]);
	}