Proportionate Final Benefit Act of 2005 - Amends title II (Old Age, Survivors and Disability Insurance) (OASDI) of the Social Security Act to provide that: (1) an individual's entitlement to any OASDI benefit shall continue through the month of his or her death (without affecting any other person's entitlement to benefits for that month); and (2) the benefit shall be payable for such month only to the extent proportionate to the number of days in the month preceding the date of death.