If I try to use Munchlax's "Snack Search" Ability and flip Tails, is my turn still over?
Yes, it is. Even if you don't flip Heads, the Ability is still considered "used".
Source: Unified Minds FAQ (2019-07-19), TPCi Rules Team (2019-08-01)

Relevant cards

Note: All applicable cards may not be listed below.
SM11_173
SM11_173