select [ShipDate], SUM([TotalDue]) Total from Sales.SalesOrderHeader
 where [ShipDate] between '2005-08-1' and '2005-08-31'group by [ShipDate]

select soh1.ShipDate, SUM(soh2.TotalDue) from
   (select distinct ShipDate from sales.SalesOrderHeader
        where ShipDate < '2005-09-01' and ShipDate >= '2005-08-01') as soh1
   join sales.SalesOrderHeader soh2
        on soh2.ShipDate <= soh1.ShipDate and soh2.ShipDate >= '2005-08-01'
   group by soh1.ShipDate order by soh1.ShipDate

;with soh as (
    select ShipDate, sum(TotalDue) as TotalDue
    from Sales.SalesOrderHeader
    where ShipDate between '20050801' and '20050831'
    group by ShipDate
)
select ShipDate, sum(TotalDue) over(order by ShipDate) as Total
from soh