One possible option in this case would be to toggle off the autorange of the control, and set the step manually for the YAxis. However, this would only work for numeric values.
Another option would be to manually set the labeld, as shown in the code snippet below:
Chart1.DefaultView.ChartArea.AxisY.TickPoints.Label = "CustomValue";
I hope this gets you started properly.
the Telerik team
Browse the videos here>>
to help you get started with RadControls for Silverlight