Note to Intuit readers: this thread contains two problems, so, for clarity:
1. TT rounds amounts on worksheets and other forms *before* doing arithmetic on them. This is contrary to instructions from the IRS, which say *not* to do rounding during data entry for calculations, only on the result. They require this for exactly the reason that has bitten some of the forum commenters due to rounding the initial numbers, i.e. that it breaks the calculation. This is a bug that still needs to be fixed.
2. Whether to round amounts ever is something the IRS has flexibility on. The failure of TurboTax to provide behavior consistent with what the IRS accepts is clearly causing problems for customers, so TT should likewise not round everything unless requested to - and *never* during calculations.
There are numerous forum discussions on this subject full of customers pointing to the IRS instructions. (e.g. for the 2023 tax year (current tax prep season), see https://www.irs.gov/instructions/i1040gi#en_US_2023_publink24811vd0e4579 )
