You can get to Form 2210 by double-clicking on Form 1040 penalty line then double clicking again on the worksheet penalty line to see Form 2210. From what I've seen Form 2210 doesn't appear in the forms list by default unless you've gone thru the deeper Annualized Income (AI) process for uneven tax by quarter.
$6 isn't an TT estimate it's a final calculation using Form 2210 which is pretty straightforward. Presumably IRS checks it. Underpayment penalty rate is currently 8%. You can also have IRS calculate it and send you a bill, but not worth it for small penalty easily calculated with your return and be done with it.
