Common/Calculator/Tax.php
public function multiply($quantity)
    {
        $this->base = round($this->base * $quantity, $this->precision);

        return $this;
    }
public function multiply($quantity)
    {
        $this->base = round($this->base * $quantity, $this->precision);

        return $this;
    }
Multiply the tax (base).

@param float $quantity

@return Tax