I hope your dataset uses SQL.
I would "unpivot" the data by writing a 5-part UNION SELECT, e.g.
SELECT Product_Name , 1 AS Month , SalesMonth1 AS Sales
UNION ALL
SELECT Product_Name , 2 AS Month , SalesMonth2 AS Sales
UNION ALL
...
SELECT Product_Name , 5 AS Month , SalesMonth5 AS Sales
Then in the SSRS Chart definition:
Month = Category Group
Product Name = Series Group
Sales = Values
But the real real answer is that your data is probably not in a useful shape for reporting. Will there only ever be 5 months? I suspect not...