Theoretically, if you paid your taxes "unevenly" throughout the year (not enough early on) or you earned your income unevenly throughout the year, an underpayment penalty could be assessed because the IRS thinks you didn't pay enough in a timely manner. I know, doesn't seem like it should be fair and the fee should be waived since you paid enough overall. Not sure if there's a way to get this waived now. Wish I could be more help.
