I sent an email over the weekend to
DCL regarding this same question. They responded with:
All transactions are in U.S. dollars (USD). Guests can present any type
of currency to settle the onboard account; however, it will be exchanged
to U.S. dollars and then posted. Currency exchange is available at Guest
Services. There is no transaction fee to exchange currency onboard. The
rate of exchange can fluctuate; therefore, Guests should check once
onboard the ship.
There is no limit to the amount of money that can be exchanged onboard.
However, in order to complete a foreign currency exchange, the Guest
will need to be traveling with Cash, Check and/or Travelers Checks. A
currency exchange cannot be done with a credit card since Guests are not
able to obtain a Cash Advance onboard.
The following types of currency can be exchanged onboard:
Dollar: Australia (AUD), Canada (CAD), United States (USD), Cayman
Islands (KYD), Hong Kong (HKD)
Euro: European Union (EUR)
Franc: Switzerland (CHF)
Kroner: Denmark (DKK), Norway (NOK), Sweden (SEK)
Peso: Mexico (MXN)
Pound (Sterling): UK (GBP)
Real: Brazil (BRL)
Yen: Japan (JPY)
During the Transatlantic and Mediterranean sailings, the currencies
listed above can be exchanged to Euros.