JQuery is changing checkbox value but the checkbox is not displaying as checked

With .attr() you set the value of an attribute in the DOM tree. Depending on the browser, browser version and jQuery version (especially 1.6), this does not always have the desired effect.

With .prop(), you manipulate the property (in this case, ‘checked state’). I strongly recommend using .prop() in your case, so the following will toggle correctly:

$(this).find(".cbx input").prop('checked', true);

For further information, please refer to the documentation of .prop().