Unless you really screw up[1], or are intentionally trying to screw the IRS[2], you don't have to worry about an audit. The IRS's goal isn't to bring down their wrath upon you, their goal is to accurately collect the taxes they are due. If you pay too little, they'll ask you to pay the difference. If you pay too much, they'll refund it. Really: I once used the single-payer tax table instead of the filing-jointly tax table, and they sent me a nice letter explaining my error alongside a big check.
[1] http://achewood.com/index.php?date=02102004
[2] http://achewood.com/index.php?date=02272003