Let's first create a table with dummy data:
Create Table CUMULATIVESUM (id tinyint , SomeValue tinyint)
Now let's insert some data into the table;
Insert Into CUMULATIVESUM
    Select 1, 10 union 
    Select 2, 2  union
    Select 3, 6  union
    Select 4, 10 
Here I am joining same table (self joining)
Select c1.ID, c1.SomeValue, c2.SomeValue
From CumulativeSum c1, CumulativeSum c2
Where c1.id >= c2.ID
Order By c1.id Asc
Result:
ID  SomeValue   SomeValue
-------------------------
1   10          10
2   2           10
2   2            2
3   6           10
3   6            2
3   6            6
4   10          10
4   10           2
4   10           6
4   10          10
Here we go now just sum the Somevalue of t2 and we`ll get the answer:
Select c1.ID, c1.SomeValue, Sum(c2.SomeValue) CumulativeSumValue
From CumulativeSum c1,  CumulativeSum c2
Where c1.id >= c2.ID
Group By c1.ID, c1.SomeValue
Order By c1.id Asc
For SQL Server 2012 and above (much better performance):
Select 
    c1.ID, c1.SomeValue, 
    Sum (SomeValue) Over (Order By c1.ID )
From CumulativeSum c1
Order By c1.id Asc
Desired result:
ID  SomeValue   CumlativeSumValue
---------------------------------
1   10          10
2   2           12
3   6           18
4   10          28
Drop Table CumulativeSum