I am excited about my upcoming cruise from Sydney, AU to NZ. However, and this may seem like a silly question to some, but I enjoy tipping specific crew (e.g. cabin steward) on top of any automated tipping by the cruise line. On a cruise based out of Australia, can I tip in USD, or is better to exchange that to AUD/NZD currency? I have only been on cruises where everything (excursions, gratuities, etc.) are based on the USD.