Uncheck a Checkbox using Jquery

I have a page with a list of check boxes, when a check box is checked I am updating the number of check boxes selected in side a p tag. This is all working.

The problem I have is when the user selects more than 5 checkboxes I want to use Jquery to unselect it.

This is what I have so far, the first if else works but the first part of the if doe

 $("input").click(function () {

        if ($("input:checked").size() > 5) {
            this.attr('checked', false) // Unchecks it
        }
        else {
            $("#numberOfSelectedOptions").html("Selected: " + $("input:checked").size());
        }

    });

Any ideas?