You can create a simple custom field to report the total amount your company has sold to an account:

Data Type                        Roll-Up Summary                         
Summary Type                SUM
Summarized Object        Opoortunity
Field to Aggregate           Opportunity: Amount
Filter Criteria                    Won equals True

This "Sales" field can then be displayed on accounts.

What I am looking to do is enable this to roll-up the hierarchy so if you have Account X with children (sub accounts) Y and Z you can see Y and Z's combined sales in the X account profile.

Any thoughts on how to do this with advanced formulas?

Best