One of the habits that I have developed, especially while developing date driven reports is to add this code to every stored procedure that I create:

--Include the entire End Date (Set time to 11:59)

 Select @EndDate = DateAdd(d, 1,@EndDate)

 Select @Enddate = cast(convert(varchar, @EndDate,101) as datetime) 

 Select @EndDate = DateAdd(s,-1,@EndDate)

--This is usually done in one statement, I broke it out for readability.

--Convert Start Date to midnight

 SELECT @Startdate = cast(convert(varchar, @StartDate,101) as datetime) 

This gives the full date range.