As anecodtal evidence that may help you quest for sleep, i am aware of some people that have been audited by Revenue as part of a routine audit.
The consensus is that while the actual audits themselves are a pain, they are usually conculded quickly where the person keeps correct records and are not trying to "put one over on the tax man".
If you have some serious errors in your books and are concerned about that then speak to your accountant ASAP and consider the voluntary disclosure as mentioned above.
And if you are notified of an audit, get professional advice!