I thought it might be fun to give you a word of the day (when I remember). Today's word is:
quinquennium: a period of five years.
This comes from the Merriam-Webster's Collegiate Dictionary, 11th edition.
I know you were looking for a word to express every 5 years. I mean, come on, we have century for 100 and decade for 10. It only seems fair that 5 years has a word. And we are deficient in words beginning with Q. So, there you go. Try using it today in a sentence. You'll feel smarter. ;-)