How to store multiple values in a profile field (specific to each users)?
You might be best installing content profile as this will allow you to use cck, when creating the profile field amount you can set it to unlimited which would allow you to store multiple values in an array for a single field. 

The total would be another dynamic field which is calculated by adding the values from the amount array each time they are changed via a hook

To add the field to a content profile, follow the below steps:


Edit the profile content type 
Go to manage fields
Add a new "text field
Fill in field details
On this page you will see a "number of values" option, choose "unlimited"


You can update content profile fields as below, just put it in a custom module or something:

//load current user
global $user;
//find the users content profile
$uid = $user-&gt;uid;
$node = content_profile_load(profile,$uid);
$pid = $node-&gt;nid;
$node = node_load($pid);
//update the field AMOUNT
$node-&gt;field_AMOUNT[0]['value'] = $var1;
$node-&gt;field_AMOUNT[1]['value'] = $var2;
//do the same for the TOTAL with calculations
$node-&gt;field_TOTAL[0]['value'] = $var1 + $var2;
//save the content profile node
node_save($node);