You got my Excellent! I've seen quite a few procedures, but I really appreciate your methodology: you paved a complete road from the ground up with concise and adequate explanations....

You might try this:

 

WHERE   salesdate BETWEEN CONVERT(DATETIME, @p_fromsalesdate) and CONVERT(DATETIME, @p_tosalesdate)

            and (@p_sitecode is null or siteglobalcode = @p_sitecode)