When Cindy Hockenberry and her husband sent in a tax-penalty payment in 2007, they knew there was a chance their math might not jibe with the IRS’s. When that turned out to be true and the amount was much higher than expected, they decided to dispute it. Fortunately for them, Hockenberry’s a pro. As tax research coordinator at the National Association of Tax Professionals, she spotted a glitch in the IRS’s calculation.