Should POST data have a re-try on timeout condition or not?

Should POST data have a re-try on timeout condition or not?

When POSTing data - either using AJAX or from a mobile device or what have
you - there is often a "retry" condition, so that should something like a
timeout occue, the data is POSTed again.
Is this actually a good idea?
POST data is meant to be idempotent, so if you
A. make a POST to the server, B. the server receives the request, C. takes
time to execute and D. then sends the data back
if the timeout is hit sometime after C. then the next retry will send data
that was meant to be idempotent.
The question then is that should a retry (when calling from the client
side) be set for POST data, or should the server be designed to always
handle POST data appropriately (with tokens and so on), or am i missing
something?