The current coordinaterounder transformer only rounds coordinates to the nearest value, while the attributerounder does offer the possibility to set the Round-off Direction to UP, Down or Nearest.
Some GIS software (like Hexagon gTechnology) rounds coordinates down internally, to a certain decimal (set in the gTechnology setting) when it validates connectivity.
Because the coordinaterounder transformer cannot round coordinates down, FME cannot produce the same results as gTechnology when checking the connectivity.