The cart page doesn't have all the values for a SKU but I can bring them in, it's just totalling them that is the problem.
Below is the code I'm using. I'm not sure where I'm going wrong.
[%set [@^rrpsavingtotal@] %]0[%/set%] // initial set up of variable for storing total
[%product sku:'[@SKU@]';%][%param *body%]
[%set [@rrpsavingprice@] %][@save_price@][%/set%] // get price difference
[%set [@^rrpsavingtotal@] %][%calc [@rrpsavingtotal@] + [@rrpsavingprice@] /%][%/set%] // add this SKUs price differnece to total
[%/param%][%/product%]
