The money datatype stores data to four decimal places for accuracy of rounding and multiplication, but only displays two decimal places because, well, because we don't deal in anything less than pennies. That's why because.
Cast the datatype to decimal (20,4) or some such thing if you really need four places.
By the way, here is a little known fact: the maximum value that can be stored by the money datatype is exactly equal to Bill Gate's net worth. The more you know....
If it's not practically useful, then it's practically useless.