dor categorical data, you have nearest neighbour or majority as the best choices... neither should change the values. I suspect you are not setting cell size appropriately and/or the extent or other settings. Rea the help and don't use the defaults unless you know they are appropriate for your situation.
by default it takes 1/250 of the width. that is not appropriate in most cases... it is something that you have to determine based upon consideration of what other data you intend to use and your inter-point spacing that is being used in the interpolation