Ok, so I have got the query to work by using a subquery seen below:
SELECT CHARTDATA2.SALES_PERSON_ID, CHARTDATA2.EMPL_LAST_NAME, CHARTDATA2.JE_PERIOD_ENDING_DATE, CHARTDATA2.metMonth, CHARTDATA2.metYear, CHARTDATA2.TOTAL_SALES, (SELECT Sum(TOTAL_SALES) FROM CHARTDATA2 AS Q WHERE Q.EMPL_LAST_NAME = CHARTDATA2.EMPL_LAST_NAME AND q.metYear=CHARTDATA2.metYear and q.JE_PERIOD_ENDING_DATE <=CHARTDATA2.JE_PERIOD_ENDING_DATE) AS RunTotal
FROM CHARTDATA2
ORDER BY CHARTDATA2.EMPL_LAST_NAME, CHARTDATA2.JE_PERIOD_ENDING_DATE;
Now the problem is that when I try to use it in a chart it is saying that a multi-level group by clause is not allowed in a subquery. I have looked on the forum for a solution to this but I am extremely new to subqueries and don't really understand what they mean. Could you help me please!