code: public function round(): void
      {
          $this->unit = Money::round($this->unit, $this->currency);
          $this->gross = Money::round($this->gross, $this->currency);
          $this->discount = Money::round($this->discount, $this->currency);
          $this->base = Money::round($this->base, $this->currency);
          $this->total = Money::round($this->total, $this->currency);
          $this->tax = Money::round($this->total - $this->base, $this->currency);
      }
docs: Rounds the amounts.