Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/MathTrig.php
public static function MROUND($number, $multiple)
    {
        $number = Functions::flattenSingleValue($number);
        $multiple = Functions::flattenSingleValue($multiple);

        if ((is_numeric($number)) && (is_numeric($multiple))) {
            if ($multiple == 0) {
                return 0;
            }
            if ((self::SIGN($number)) == (self::SIGN($multiple))) {
                $multiplier = 1 / $multiple;

                return round($number * $multiplier) / $multiplier;
            }

            return Functions::NAN();
        }

        return Functions::VALUE();
    }
public static function MROUND($number, $multiple)
    {
        $number = Functions::flattenSingleValue($number);
        $multiple = Functions::flattenSingleValue($multiple);

        if ((is_numeric($number)) && (is_numeric($multiple))) {
            if ($multiple == 0) {
                return 0;
            }
            if ((self::SIGN($number)) == (self::SIGN($multiple))) {
                $multiplier = 1 / $multiple;

                return round($number * $multiplier) / $multiplier;
            }

            return Functions::NAN();
        }

        return Functions::VALUE();
    }
MROUND.

Rounds a number to the nearest multiple of a specified value

@param float $number Number to round
@param int $multiple Multiple to which you want to round $number

@return float Rounded Number