Does the app support multiple currencies?

Unfortunately, it is not possible to display the Shipping Rate in a currency other than the default currency you have selected for your store.

Even if you enable multiple currencies for your store and a customer chooses to display product prices in a different currency, any Shipping Rates from the Postcode Shipping app will display in your store's default currency because the Shipping Rate is added on to the order total after Shopify has done the currency conversion.