I'd like my column scatter graph to have symbols moved up or down a bit so points with approximately the same Y level are plotted in a straight horizontal line?  

When making column scatter (dot plot) graphs, Prism doesn't put the dots into bands that are aligned horizontally. Instead, each point is centered on its actual Y value. Some programs move points up or down a bit to make the graph look nicer, but this means that the Y values are only approximately correct. Prism plots the exact Y value.

To get the effect you want, transform your Y values using a user-defined transform to round values. Use this transform, and set the parameter 'Round' to an appropriate value:

Y=int((Y+(Round/2))/Round) *Round 

If your Y values are 3, 8, 11, 15, 19, 21 and you set Round to 10, then this transformed results will be 0, 10, 10, 20, 20,20. If you set Round to 2, then the results will be 4, 8, 12, 16, 20 and 22.