Calling all crosstab gurus...Running-Total troubles

[JGirl]

What I'm trying to create:
I'm trying to create the following crosstab structure in a report studio report (relational model):

Rows are dynamic based on dates.  Columns are both dynamic (for products) and fixed (last 3 columns - the aggregates).

	Tents	Bug Spray	Knife	...	Total Qty	Total $	Cumulative $
2009-01-01	1	30	5	...	36	$360	$360
2009-01-02	1	2	15	...	18	$180	$540
2009-01-03	2	15	17	...	24	$240	$780
...	...	...	...	...	...	...	...

What I've tried:
Ive created a crosstab with the dates creating rows, the products creating columns, and the aggregate quantity.  Easy enough.

Then I drag the [Sales $] as another column to the crosstab.  Also easy enough, and works as expected.

Then, I drag a query calculation as another column to the crosstab, and define the value as running-total([Sales $]).  And this is where it all goes wrong!

The first row is correct (eg. Shows $360).  The second row is correct (shows $540), and beyond that the numbers are much higher than I would expect, and also in the wrong order (so not accumulating in the same order as the dates in my report).

What I need:
I'm guessing that I need to specify some additional properties, aggregation levels and/or rollup types for the running-total calculation, but i've tried a lot of combinations and i just can't get it right.

Is anyone able to shed any light on what is going wrong, and how i can fix it?