It is possible but there are ways to prepare for the audit as well as defenses. You are dealing with the State Department of Revenue so you should comply.
"What the Auditor Will Want to See
The auditor will want precise odometer readings. They will also consult trip logs, DOT records, and the reported IRP miles. They will use this to determine as precisely as possible how many miles were actually driven, and compare this with the receipts submitted by the driver. If there is a discrepancy between the two, then the auditor will assess how much tax should have been paid.
In the past some drivers have tried the “Sorry, but I lost those receipts” response. That's not a good idea. The auditor will simply do his or her own estimate of what is owed, and there's a good chance that the driver will not be happy with the figure. And of course the tax collector can always levy fines against anyone who doesn’t cooperate fully with the investigation.
If this doesn’t sound like much fun, that’s because it’s not.
Your Best Defense is Complete, Accurate Records
Most auditors aren’t out to get owner-operators or fleet owners. They just have a job to do and they’re very serious about doing it correctly. Hopefully you’ll never have to deal with an audit. But if you do, you can’t go wrong when you have trucking business software in your corner. It accurately calculates the exact number of miles driven per state, and records it in a clear, easy-to-understand format. So if the tax collectors do come knocking, you can face them with confidence, knowing you have all your ducks in a row." http://www.getloaded.com/load-board-blog/post/How-to-Survive-an-IFTA-Audit
Where in Wisconsin are you located so I can provide a link for Attorneys in your area that specialize in these matters that provide FREE consultations?