Joshua,
Microflows are treated as one transaction by Mendix - see documentation here. In particular, see the portion of this documentation that describes custom error flow options for information about how to proceed with your microflow in the event of an error.
For more fine grained control of what does and does not get committed or rolled back, the Community Commons module contains a number of functions that enable you to explicitly begin and end transactions within portions of a microflow (StartTransaction and EndTransaction) as well as checking to see what Objects or Members have been changed (look in the ORM folder for several of these).
Hope that helps,
Mike