|   | 1 |  initial version  | 
You are correct that this should work now in recent versions. Check out link text and search for the word 'ticks'. I don't have your original function $f$, but it shouldn't be hard to create.
sage: plot(x^2, (x, 2, 12), ticks=[[3,6],None])
We need to get this in plot? ... :(
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                Copyright Sage, 2010. Some rights reserved under creative commons license. Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.