Hi,
Assuming I understood what you need correctly you wish to have a "Total" calculated column that calculates several other % columns.
If so - you have 2 options for doing this (assuming normal calculated column does not do the trick for you):
1: Develop a synch event handler that on each itemadding and itemupdating will calculate in code all the other columns into a new column (make it read only so users will not see that column in new/edit forms).
2: No-Dev solution: you can indeed open SharePoint designer and craete a custom workflow that run for each item change / created. Do the calculation you need in a workflow variable, and store the result in the "Total" column.
If I did not understand - please ellaborate further on your requierments and post again (and sorry in advanced),
Thanks,
Shai Petel,
KWizCom
Shai Petel (Ben Shooshan)
KWizCom SharePoint Advisor
MCTS for SharePoint, MCT
http://www.kwizcom.com