Use these two queries for running sum.  You could change the criteria so that
it gives a running sum of the last 5 entries like this in second query --
WHERE (((Running_Sum_1_1.Rank) Between [Running_Sum_1].[Rank] And
[Running_Sum_1].[Rank]-4))

   Running_Sum_1 ---
SELECT Q.[Date close], Sum(Q.x) AS SumOfx, (SELECT COUNT(*) FROM [Change
Requests] Q1
     WHERE Q1.[Date close] < Q.[Date close] )+1 AS Rank
FROM [Change Requests] AS Q
GROUP BY Q.[Date close]
ORDER BY Q.[Date close];

SELECT Running_Sum_1.[Date close], Running_Sum_1.Rank,
Sum(Running_Sum_1_1.SumOfx) AS [Running Sum]
FROM Running_Sum_1, Running_Sum_1 AS Running_Sum_1_1
WHERE (((Running_Sum_1_1.Rank)<=[Running_Sum_1].[Rank]))
GROUP BY Running_Sum_1.[Date close], Running_Sum_1.Rank;