If you make sure that the date field has values that are proper dates then they will sort properly if you don't override the sorting in any way.
Check to see if the field contains the dates as actual dates and not just as textual dates. You can check that in your Data Model Viewer by looking at the tags and see if the field has the tags $date and $timestamp.
To ensure that textual dates come in as real dates you can do this in your load script:
LOAD ..... Date( Date#( SalesDate , 'DD-MMM-YYYY' ) AS SalesDate, ......