Generally, people seem to say either true or .5 size small.
My feet are standard width ("D") and I went up .5 size because my big toes were hitting the ends of the shoes in my true size. I suppose it's just the way the toebox on the IV is cut.
Anyway, my recommendation is:
-if you have narrow feet, your true size would probably be fine (be sure to factor in if you like a snug fit or a little space; if you like a little space, just go with .5 size up).
-if you have standard width or wider feet, go .5 size up. This should give you the extra room you might need and if not, a little extra room in these shoes is better than not enough room.