I'm seeking advice on how to best capture monthly sales in Salesforce by a sales team that each have multiple accounts.  We are only looking for monthly total revenue by representative at this point.  

Currently, I have to create a new monthly  Opportunity each month (closed won) for each Account to capture monthly sales and then create dashboards and sales data tracking within Salesforce.  I'm sure there is a better way that doesn't necessitate creating monthly Opportunities per Account.  Clearly that messes up staging and pipeline.

Of course I can do this simply in Excel, but it would be great to utilize the power of Salesforce and share this data across the sales teams using Salesforce.

We're using the Professional edition.

Any help will be appreciated.

Thanks.