Excerpt from the RCI website:
Value-Added Tax (VAT)
On select itineraries we are required by the local law to collect value added tax (VAT) on select onboard purchases. The tax will be added at the time of purchase onboard. The VAT requirement is applicable to itineraries that sail only to European Union* ports of call.
Travelers from countries outside of the European Union are eligible for a VAT refund on select purchases they make within the European Union.