I emailed Carnvial and this is what they told me about tips on the Sensation:
Sent: Monday, December 03, 2001 4:08 PM
Subject: RE: Contact Us [GFC2001120300000047]
Thank you for visiting Carnival.com. In regards to your query, the tips
are still done with cash at the end of the cruise. If there is anything
else I can do for you please don't hesitate to ask and thank you for
choosing Carnival Cruise Lines.