The IRS likes round numbers, i.e. just dollars, not cents. Just round up or down to the nearest whole number.
You should be able to enter any number, though. Go To:
Federal Taxes > Deductions & Credits > Cars and Other Things You Own
Add/Edit or Revisit Car Registration Fees (see screenshot)
In some cases, you are better off deleting a whole form with the "trash can" icon and re-entering manually.
