> but we immediately delete it once we have summed all of the round up change.

Ah, that puts a different spin on it. You do have access to all transactions - but you claim not to store them.

It's an interesting idea - and I hope you can convince people to donate more to charity - but I would feel uncomfortable giving you access (albeit read-only) to every transaction I make.

Perhaps this is a model which is best suited to selling directly to banks?