Quotes from different IRS publications:
“For electronic filing, the IRS requires all amounts that are transmitted individually to be rounded.”
“You can report on line 1a (for short-term transactions) or line 8a (for long-term transactions) the aggregate totals from any transactions (except sales of collectibles) for which:
You received a Form 1099-B that shows basis was reported to the IRS and doesn't show any adjustments in box 1f or 1g;
If you choose to report these transactions on lines 1a and 8a, don't report them on Form 8949. You don't need to attach a statement to explain the entries on lines 1a and 8a and, if you e-file your return, you don't need to file Form 8453.”
So, all these separate transactions on line 1a and line 8a are not transmitted with e-filing! So, they can be added on cents basis: Only the totals of proceeds, costs and gains are transmitted and, as such, only these totals should be rounded.
All other transactions still have to be reported with proceeds, cost and gain on the different 8949s and all these amounts will be rounded to the nearest dollar. So, these transactions will still result in a rounding error, which, however, should be much smaller than if all transactions would be reported on 8949s, because, normally, almost all transactions have no adjustments in box f or 1g, and are reported on line 1a or 8a, and, therefore, do not have to be transmitted with e-filing.
Here I think is where the problem lies: TurboTax seems to transmit all transactions with e-fling. Therefore all amounts, proceeds, cost, and profit, of all transactions have to be rounded with TurboTax. If they would stop transmitting the data on the individual transactions reported on line 1a and line 8a, as allowed by the IRS, they can go back to adding the 1a and 8a transactions on a cent basis before rounding and most of the rounding problem will be gone.
TurboTax suggested this solution already by stating that you could do this by entering your 1099-B manually as indicated above. You would still be able to e-file without attachments.
