What currency is used when displaying the price of gems? Is it USD or is it automatically adjusted for whatever country you select?
According to the GW2 Support page on Gems,
When you open the Gem Store billing interface, you will be asked to select your country. Prices will be presented in the currency associated with the country you selected. You will be required to enter a billing address that matches the country you selected to complete the purchase. You may change your country at any time. Gems may be purchased using Euros, U.S. Dollars, or British Pounds.