Does this get you closer?

SELECT CONVERT( CHAR(10), sosb_CarDetail_DateReleased, 101 ) AS [DateReleased]

, Count( sosb_CarDetail_CarNumber ) AS TotalCarsByDate

, sosb_SP_Description

, Round( Sum( sosb_CarDetail_NetTons ), 2 ) AS Total_NetTons

FROM #mytable

GROUP BY CONVERT( CHAR(10), sosb_CarDetail_DateReleased, 101 )

, sosb_SP_Description

ORDER BY CONVERT( CHAR(10), sosb_CarDetail_DateReleased, 101 ) DESC

SELECT Datepart( Month, a.DateReleased ) AS MonthReleased

, Sum( a.TotalCarsByDate ) AS GrandTotalCars

, sosb_SP_Description

, Sum( Total_NetTons ) AS TotalNetTonsByMonth

FROM ( SELECT CONVERT( CHAR(10), sosb_CarDetail_DateReleased, 101 ) AS [DateReleased]

, Count( sosb_CarDetail_CarNumber ) AS TotalCarsByDate

, sosb_SP_Description

, Round( Sum( sosb_CarDetail_NetTons ), 2 ) AS Total_NetTons

FROM #mytable

GROUP BY CONVERT( CHAR(10), sosb_CarDetail_DateReleased, 101 )

, sosb_SP_Description ) a

GROUP BY Datepart( Month, a.DateReleased )

, sosb_SP_Description