Rounding can be very tough, especially for visual learners. I have used this anchor chart with my students for the past 3 years and found it is the biggest bang for your buck when it comes to reaching the most students. Having worked most with ESOL and ESE students, this has worked better than any rhyme or rule I have tried in the past.
Print out on 11x14" paper and show students how if you drop a ball past the "50's" it will roll forward to the next hundreds place. Explain if you drop it before, it will roll back to that same hundred. And of course if it lands on the 50's it would techinically not move, but let's face it, everyone wants to roll to more, not less, so the 50's roll forward.
This document includes one anchor chart for classroom use and smaller versions for students to keep in their notebooks.
ALL of my students were so mastered at this skill by the time FCAT rolled around, they were able to draw out their own rolling hills number line on their test and round it that way.
PLEASE CHECK OUT MY "ROUNDING MADE EASY BUNDLE" THAT COVERS ROUNDING TO 10'S, 100'S AND 1,000'S.
CCSS.Math.Content.3.NBT.A.1 Use place value understanding to round whole numbers to the nearest 10 or 100.
CCSS.Math.Content.4.NBT.A.3 Use place value understanding to round multi-digit whole numbers to any place.