I have my students underline the place they are rounding to - then they circle the neighbor to the right. I classify the circled # as either weak (0-4) or strong (5-9). Then, above the number we write our stay/weak answer and our go/strong answer. Then they circle the correct annswer after looking at the circled "Boss".
I have found with my students that if they only have two answers to choose from it is much easier for them that is why I have them write the two possible choices - they eventually don't need to do that but in the beginning it helps.
40 50
48 Picture the 4 underlined and the 8 circled - 8 is a big strong boss so we go to 50.
If it was 248 and rounding to the nearest tens we talk about how the number to the left tags along in the answer (like a puppy, etc...)
Hope this helps