Agreed "You can round off cents to whole dollars on your return and schedules", but not Form 8949. You can do the rounding on the final total of all 8949 pages and carry it over to Schedule D. That's what TT did in the past.
Now go back to the given example: $1.39 becomes $1 and $2.50 becomes $3.
Assume this is a profit transaction, the filer has a gain of $2 (3-1) instead a gain of $1 (2.50-1.39).
If there are 100 rounding transactions like this, the filer would pay a capital gain of $200 instead of $111.
An extra capital gain of $89 the filer has to pay tax on.
If the situation is reversed, it would be an extra capital loss of (89). I don't think the IRS would overlook this discrepancy when comparing with the reported 1099-B.
