Here is a catchy rhyme you can use with your kids who are having trouble remembering how to round numbers:
Find the place and look next door,
Five or higher, add one more,
Four or less, let it rest.
I have this made into a small 9 x 12 poster and it is posted in my room. I refer to it the first time I teach rounding for the year. All the kids recite it with me and we do several examples using it with different place values being asked. Later on, when the kids forget (and they will!) I point to the poster and tell them to use the "rounding rule." Eventually, all I have to do is point. What is really funny is when the other kids point to the poster when their friend they are helping forgets.