Not really as 'elegant' as set analysis... but maybe this helps:
if(floor(monthend(date(date#(AU_date, 'MM/DD/YY'), 'DD/MM/YYYY'))) = date(date#(AU_date, 'MM/DD/YY'), 'DD/MM/YYYY'), sum(Value))
This gives only the result of the value on the last day of the month ... I think that's what you mean.
(In data handling of the bar chart, you can choose to surpress the null values)