First, it's unlikely your business will be selected at random for an IRS audit. If you should get so lucky, congrats. Please engage a tax attorney or CPA. The statute of limitations for IRS audits is three years after filing, or the due date, whichever is later. The IRS can go further back if they catch a substantial error, or if you failed to file (or fraudulently filed) a return. Since you're supposed to retain IRS payroll files for four years, you shouldn't run into a problem.