public function netTotal($format = true)
    {
        $total = 0;

        if ($this->count() != 0) {
            foreach ($this->getItems() as $item) {
                $total += $item->netTotal(false);
            }
        }

        if ($total < 0) {
            $total = 0;
        }

        return $this->formatMoney($total, null, null, $format);
    }