US Chess has historically used integer ratings. However, we do all internal ratings computations in floating point.
This means that someone who had a slightly positive result would gain at least a full point and someone who had a slightly negative result would lose at least a full point.
The Ratings Committee and Executive Board decided that we should save those floating point ratings in between events, so this change was made effective with events that ended on September 18, 2014.
However, official published ratings are still kept as rounded integers. This means that someone whose rating in floating point is 1999.50 or greater will be rounded up to 2000 for official ratings purposes, including peak rating based floors.