I was just asking because the last sentence in your opening post is confusing…
As I read this sentence, I thought you wanted some dimensions rounded and some untouched…
Now it is clear that you want all dimensions rounded to the nearest 0.5 mm!
It is a common misperception that SketchUp rounds the dimensions to the set value, but in fact this is just display precision!
No dimensions are rounded, only the displayed dimension is rounded to the set value.
This misconception can lead to errors, because it behaves different than people are expecting.
See this old thread: Dimensions of components add up to total dimension yet a gap exists
And this one: Dimensions don't add up