Interesting Math Problem

[BEES INC]

I've been awfully busy programming lately. My Django-based side
project is coming along well and I hope to have it ready for use in a
few weeks. Please don't ask more about it, that's really all I can say
for now. Anyways, I came across an interesting little math problem
today and was hoping some skilled programmers out there could come up
with a more elegant solution than mine.
Problem: Star Ratings

People can rate cheeseburgers on my website with a star rating of 0-5
stars (whole stars only), 5 being mighty tasty and 0 being disgusting.
I would like to show the average of everyone's ratings of a particular
cheeseburger to the nearest half star. I have already calculated the
average rating as a float (star_sum) and the total number of people
that rated the particular cheeseburger (num_raters). The result should
be stored as a float in a variable named "stars."
My Solution (in Python):

# round to one decimal place and
# separate into whole and fractional parts
parts = str(round(star_sum/num_raters, 1)).split('.')
whole = int(parts[0])
frac = int(parts[1])
if frac < 3:
___frac = 0
elif frac > 7:
___frac = 0
___whole += 1
else:
___frac = 5
# recombine for a star rating rounded to the half
stars = float(str(whole)+'.'+str(frac))

Mmmm… In-N-Out Burgers… Please reply if you've got a better solution.