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...