You absolutely get paid for completed months of service. I know this b/c I am getting my deposit for 8 years and 11 months next week. Kicker is you don't get partial month credit, so I am five days shy of my 9 years, something I could have done better had I realized at the time...
I also know this because I have the original release message for the Force Shaping 07 board. It is dated 26 Jul 06 and your MPF should be able to pull it up. Check Part IV, section 19, para A. "Each full month of active military service that is in addition to the number of full years...will be counted as one-twelth of a year."
Your MPF actually enters in your DD214 the amount of time your speration pay is based on. Finance can't argue with that or the offical release message.
It all used to be posted on the website below but everything is updated for 08. Search around you may still be able to find the old messages online - if not local MPFs should have records. The calculator link shows where you enter months also.
Don't let the finance weanies still your money b/c they are not smart enough to do thier own jobs.
Hope it helps...
http://ask.afpc.randolph.af.mil/forceshape/