I got my true size in the Penny Foams and initially thought they were too small. However, the more I wore them, the shoes broke in and now they fit great. I'm glad I didn't go up .5 size.
If you can, try the Foams on before you buy them. If you can't, you should be fine with your true size as long as your feet are standard width ("D"). If you have wider feet, .5 size up is probably smart.