Going back to 2009, there is a forum discussion of this issue at http://www.telerik.com/forums/two-way-rating-precision. The response at the time indicated that a change was coming, but I have since learned that this change never happened. If I set Value="2.5" and Precision="Item", the Value is rounded to 3. It should be possible to allow users to rate only a whole number of stars (Precision="Item"), but if the Value is set to a decimal, it should display the fractional result.
It will be possible to configure custom attributes for the items of the RadRating control, similarly to the Custom Attributes implementation for RadComboBox: http://demos.telerik.com/aspnet-ajax/combobox/examples/programming/customattributes/defaultcs.aspx
Currently the RadRating control can be used in touch devices only when its Precision property is set to Item. It should be possible to perform selection in the rating regardless of its precision.