I also have my students underline the place value being rounded, but I also make them box the number that tells them if the number rounds up or stays the same. 5 or more, raise the score. 4 or less, let it rest.
This little rhyme would help students remember how to round up decimals. It would be inexpensive to make and easily replaced if damaged. It may be difficult for the students to remember what exactly the rhyme is suggesting. Maybe you could write on the top "Rounding Rhyme" to help them remember.