I know most people won't be interested, but I have found out more about how social security rounds. Here is what happens to my check:
PIA = $xxxx.c0 (next lowest dime)
Adjustment for starting early or late (percentage)
Medicare Part B = $zzz.e0
Net = wwww.f0 (rounded down to next lowest dime)
This net is what is rounded down to the next dollar.
After that, federal withholding and any Medicare Part D premiums are withheld.
In my case, the sequence is
PIA = xxxx.40
medicare Part B zzz.70
Rounded Down $wwww.00
This is my pre-withholding pre-medicare Part D benefit, which I will refer to as my "Benefit" with a capital B.
The withholding is now computed as the percent you have chosen, rounded off (I think) to the nearest dime (the dime part is correct).
The medicare Part D premium is also a multiple of a dime.
My deposit is then the Benefit minus withholding minus Part D premium.
This gives me the correct answer for the three different deposits* I will receive in the first four months of being in medicare, as well as for the month before medicare.
2. When to round the final monthly benefitConsider the following before rounding the final monthly benefit
the family maximum;
age (including reduction by a fixed money amount or consideration of the Retirement Insurance Benefit (RIB) limitation);
Deduction for supplementary medical insurance (SMI) premium for which the claimant is liable [this is Part B]
4. Adjustments applicable after lower dollar roundingThe following deductions or adjustments are made after lower dollar rounding
Recovery of a prior overpayment (including SSI offset) and repayment of excess overpayment refunds;
Attorney fee withholding and repayment of excess attorney fees withheld;
Deduction for Part D premium;
* They forgot the IRMAA for Part D the first two months, so they are charging me 3 premiums in month three and 1 premium in month four.