SSRS: Sum Of A Column With Subtotals Based On A An ID Group

Hello,
I'm just starting to analyze with SQL 2005 reporting services and trying to build a test report using the report wizard.

This is how i've got it in SQL reports now:

Opportunity ID Product Name Cost
--------------------- --------------------- ----------------
1 Orange $1
1 Apple $2
1 Grapes $4
2 Orange $1
2 Apple $2
3 Orange $1


Now, what if I wanted to group them to provide subtotals like:


Order Product Name Cost
--------------------- --------------------- ----------------
1 Orange $1
Apple $2
Grapes $4
-------------------------------
SubTotal $7

2 Orange $1
Apple $2
-----------------------------
SubTotal $3

3 Orange $1
------------------------------
SubTotal $1

The problem that i'm having right now is on the layout designer somehow programming the subtotals based on the IDs.
Am i thinking in the right direction that I should be using the layout designer to do this? Or should this be done programmatically?

Thanks.
Mike