Hi there @Matteo_Bersan!
This seems to be a bit more complicated than one would think. I think the below might do the trick…
IF({Input}, IF(ABS({Input} - CEILING({Input}, .5)) < ABS({Input} - FLOOR({Input}, .5)), {Input} + ABS({Input} - CEILING({Input}, .5)), {Input} - ABS({Input} - FLOOR({Input}, .5))))
This makes use of both the CEILING() and FLOOR() functions to compare which is closer to the original {Input}. I think ROUND() is looking for an integer as a precision value, where as FLOOR() and CEILING() will accept decimals.
Hope this helps! :slightly_smiling_face: