It's rare, but it is possible. For instance, when the Swiss Franc appreciated rapidly recently, choosing DCC to lock in the exchange rate would have saved money had the customer selected DCC right before the appreciation. One of the "advantages" of DCC is that the customer can lock in the exchange rate. Even if the DCC rate is 3-5%, if the local currency appreciates more than this between the transaction date and the posting date, then the customer will have come out ahead by choosing DCC. In practice, this is unlikely to happen between two currencies in developed countries with stable currencies.

I have yet to see a case with my transactions where DCC was offered where I would have come out ahead by selecting DCC.