No.
DCL has a recommended daily amount, $14.50 per day, for tips. I posted earlier in this thread who's included in that. you can either prepay that (before your cruise); otherwise, it will be added to your onboard account. If you want to tip more than that recommended amount, you can either leave cash at the end of the cruise or go to guest services and ask them to increase the amount you want to tip. It's broken down by cast member so you can adjust amounts individually.
The only thing I would say you
need cash for for tipping is luggage porters at port and room service. Everything else can be done electronically.