Round decimals up to thousandths. Should also include some whole number rounding so students can see it’s all part of the same idea. Special attention should be given to rounding up 9s. Here's a good video on that.
Watch these Khan Academy videos:
Do these Khan Academy exercises:
Next, give your students these challenges:
Conclude by leading this investigation:
Round-off Dragon by MathPickle
5.NBT.A.4: Use place value understanding to round decimals to any place.