Here are some activities to improve your rounding skills.  Have fun while you learn!

http://www.aplusmath.com/Flashcards/rounding.html (you can adjust the level to your liking)

http://www.quia.com/cc/293.html (you will like this if you like memory games)

http://www.quia.com/mc/293.html

http://www.bbc.co.uk/education/mathsfile/shockwave/games/roundoff.html (this one is good if you are looking for a challenge)