Pricing/Resolver/TaxResolver.php
protected function resolveSaleTargetCountry(SaleInterface $sale): ?CountryInterface
    {
        // Get the country from the sale's delivery address
        if (null !== $country = $sale->getDeliveryCountry()) {
            return $country;
        }

        // If none, resolves the customer's taxation target address
        if (null !== $customer = $sale->getCustomer()) {
            return $this->resolveCustomerTargetCountry($customer);
        }

        return null;
    }
protected function resolveSaleTargetCountry(SaleInterface $sale): ?CountryInterface
    {
        // Get the country from the sale's delivery address
        if (null !== $country = $sale->getDeliveryCountry()) {
            return $country;
        }

        // If none, resolves the customer's taxation target address
        if (null !== $customer = $sale->getCustomer()) {
            return $this->resolveCustomerTargetCountry($customer);
        }

        return null;
    }
Resolves the sales's taxation target country.

@param SaleInterface $sale

@return CountryInterface|null