Reports - group by date doesnt group by the date correctly

Could anybody assist me or guide me in the correct direction for what I need to do. Lets use the Detailed Sales report for example... If you place the date in the first column and group by first column, it does not group all of the same dates. I believe what it is doing is also grouping the Time as well as the date. Well of course these transactions all happened during different hours of the day, but i want it to group. by the date only, ignore the time.

what could I do to the code to modify this change? any ideas?