public function getDetalleCostosAttribute()
 {
     $str = "Sub Total: " . Helper::tm($this->sub_total) . '<br>';
     $str .= "Monto Excento: " . Helper::tm($this->monto_excento) . '<br>';
     $str .= "Monto IVA ({$this->impuesto}%): " . Helper::tm($this->monto_iva) . '<br>';
     $str .= "Monto Total: " . Helper::tm($this->monto_total);
     return $str;
 }