When I tutored elem. math and when my kids were this age, what I did was I wrote out the numbers 1 through 9 on cards. Then I spread them out sort of like a mountain, with 1 at the low end on one side, 9 at the low end on the other, and 5 at the top - the "peak" of the mountain.
I told them that when they were rounding, imagine they were climbing this mountain. If they stopped on the 1 - 4 side, then they "slid" back down the mountain to the the lower number side. If they stopped at the top (on the 5) or on the 6-9 side, they were "over the hump" so they got to "slide down" to the next higher number.
Then, I explained that it didn't matter if it was 1-10, or if it was 80-90, or 1120 - 1130, the concept was the same. Then, once they seemed to get that concept, we would expand it to show how it worked with rounding from 1 - 100 (with 50 as the "peak"), or etc...
at 9:03 AM on Nov. 12, 2009