This depends ENTIRELY on your version of xcart.
Use webmaster mode and determine the variable of the order amount.
Ah, but in version 4.1.x, you have to jump through hoops to see the variables.
I have configured LinkShare for 4.5.4 - and it was relatively easy, we just had to locate the variables -- but in 4.5.4 that is much easier than in 4.1.x
There is a way to edit a smarty file, and enable debugging and then see the variables on a page.
this may help:
http://forum.x-cart.com/showthread.php?t=31962&highlight=file%3Adebug_temp lates.tpl
or
http://forum.x-cart.com/showthread.php?t=10116&highlight=file%3Adebug_temp lates.tpl