Using the white board, draw 10 houses along a street. The house numbers are 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100. Draw a road in front of them with 10 little dashes or points between the houses. This is to show the kids the distance between the "mid-point."
Now tell the kids that a friend is coming to visit but does not know which house he needs to go to. Give him a number, such as 34. Put him at the dash on the road which would be 34. Ask your class which house he is closest two. Get students to discuss how many steps (dashes) away from number 30 and number 40 he is. Repeat with several differently numbered "friends."
Ask half the class to draw (or color in) a rocket ship and half to draw a robot. Cut these out and write a number on each of them. The rocket ships will be numbers rounded to tens and hundreds, for example 300, 20, 450, 900 and so on. The robots will be numbers that need to be rounded, for example 298, 16 and so on.
Tell the children each rocket ship needs a robot and ask them to send the robots one by one to the ship that their number can be rounded to. It will be obvious to them at first since you have made the numbers very easy. As the children begin to grasp rounding, put the numbers closer together. Also, make sure the children do this one by one and tell them to ask for help if they need it.
Line the students up and give them each a number. Try to draw the numbers on paper plates so all the other students can see. Now write a line of numbers on the floor in front of them from 20 to 170, by tens.
Each student will step up to the drawn line and you will call out two numbers on the line. They simply have to decide which number they are closer to. If it helps, ask them to stretch out their legs between the two numbers and "feel" which number is closer. Ask them to call it out and explain their choice. As the students progress, make it more difficult by choosing numbers closer together.
Once you feel your students are starting to grasp rounding, give them a surprise quiz. This quiz should have multiple choice questions and a number to round. This will allow them to progress from rounding numbers visually to doing it in their heads.