Closing a task flow with transactions, but no changes

Hi there

When using bounded task flow that use shared transactions I would like to know what is best practice when closing the task flow if no changes need to be persisted to the database.

We would like to have three buttons on our pages/fragments: Save, Cancel, Close.  The Save button flows to a TaskFlowReturn which has an End Transaction set as commit.  The Cancel button has an End Transaction set to rollback. 

We intend the Close button to simply return to the calling flow, without calling a commit or rollback.

We can enable/disable the buttons depending on the "dirty" state.

We cannot, however, put a TaskFlowReturn on the flow without setting the End Transaction setting.

My question is: would setting a rollback End Transaction on the close button result in an unnecessary call to the database?

How should this be implemented should we want the Save, Cancel and Close buttons?

Thanks in advance