When TurboTax calculates the sum of the monthly columns on Form 1095-A for the purpose of the health-insurance deduction, it appears to round the value entered for each month and then sums the rounded numbers. For example, it takes a monthly entered amount of $499.51 and calculates an annual total of $500 x 12 = $6,000.
This violates basic accounting principles and specific IRS guidance. Sums should always be taken by adding unrounded figures and then rounding the total. So in this example, $499.51 x 12 = $5,994.12, which is then rounded to $5,994. The sum should be reported as $5,994, not $6,000.
The IRS appears to agree. This is from the IRS instructions to Form 1040:
