public function round(int $precision = 0) : self
    {
        if ($precision < 0) {
            throw new InvalidArgumentException('Decimal precision cannot'
                . " be less than 0, $precision given.");
        }

        $b = [];

        foreach ($this->a as $value) {
            $b[] = round($value, $precision);
        }

        return static::quick($b);
    }