A Social Security benefit is rounded to the next lower dime at each step of the computation.  Then, if the benefit is not an even dollar amount, it is rounded down to the next lower dollar (after deduction of the Medicare premium, if any).

The procedure for rounding benefits down was one of several Social Security-related provisions included in the Omnibus Budget Reconciliation Act of 1981 (Public Law 97-35) enacted August 13, 1981. The changes in the Social  Security program were intended to help lower costs by reducing or eliminating benefits that were not essential to assuring basic income protection for beneficiaries. 

The rounding procedure provides some savings to the program without a significant loss to any individual.