code: protected function updateVatDisplayMode(SaleInterface $sale)
      {
          // Vat display mode must not change if sale has payments
          if ($sale->hasPayments()) {
              return false;
          }
  
          $mode = null;
          if (null !== $group = $sale->getCustomerGroup()) {
              $mode = $group->getVatDisplayMode();
          }
          if (null === $mode) {
              $mode = $this->defaultVatDisplayMode;
          }
  
          if ($mode !== $sale->getVatDisplayMode()) {
              $sale->setVatDisplayMode($mode);
  
              return true;
          }
  
          return false;
      }
docs: Updates the vat display mode.
  
  @param SaleInterface $sale
  
  @return bool