edit2
I have attached a drawing showing how to do this with a label style that has 4 components and a few expressions.
These expressions check for the elevation of the surface and set the text height to something visible if true, otherwise they are set to a very small height that won't be seen when plotted. These expressions are added to the contour label style section.
if({Surface Elevation}-(TRUNC({Surface Elevation}))=.5,0.01,0.0000004)
if({Surface Elevation}-(TRUNC({Surface Elevation}))=.25,0.01,0.000004)
if({Surface Elevation}-(TRUNC({Surface Elevation}))=.75,0.01,0.000004)
if({Surface Elevation}-(TRUNC({Surface Elevation}))=0,0.01,0.000004)