The auto-axis routines are changing the scaling. Set the AxisTickSpace and AxisMinorTicksPerMajor properties to 1. If the labels end up too close together, labels may get deleted from the graph to prevent overlap.
this.BuildChart();
this.XAxis.AxisTickOrigin = 0.5;
this.XAxis.AxisTickSpace = 1;
this.XAxis.AxisMinorTicksPerMajor=1;