Try it out below query, You can add more conditions as per your requirement

;WITH Sales AS

(

SELECT CostsAllocated ,

CAST(MONTH(BillDate)AS VARCHAR) +'-' +CAST (YEAR(BillDate)AS VARCHAR) AS BillDate

FROM AcFeesHistory WHERE FeeEarnerCode like 'prw' and BillDate >'2014-01-01'

)

SELECT SUM(CostsAllocated),BillDate FROM Sales Group By BillDate