SUMIF with date range

***I'm using Excel 2003***

This seems like it should be a no-brainer, but I just can't figure it out, but then again I'm not that advanced so I'm flailing away a bit here.

In column A. I have a bunch of dates in the format dd/mm/yy. In column V, I have the corresponding sales figures. In column W, I'm trying to code a formula that will sum all the sales for the month. So when the end of the month comes along the total sales for that month will be calculated in column W. The catch is that, since this sheet will be used for different years, the row where the end of months occur are not none ahead of time, so I have to refer back to column A to find the end of the month. There are also blank cells in column V.

Here's one formula I've tried without any success. The first part finds the end of month with no problem, but the SUMIF portion doesn't work.
=IF(A5=WORKDAY(DATE(YEAR(A5),MONTH(A5)+1,1),-1),SUMIF(MONTH(A1:A7),MONTH(A5),V5:V4244,0)

Col A------Col V------Col W
1/2/15-----$15-------Blank
1/15/15----Blank-----Blank
1/23/15----$10------Blank
1/30/15----Blank-----Blank
1/31/15----$15------$40
2/1/15-----$25------Blank
2/7/15-----$10------Blank

(Apologies for rough sketch, but table feature was not working properly)