Don't know if its the best way, but here is what I did.
function openCloseAll(){
if($('h3').hasClass('ui-collapsible-heading-collapsed')){
$('h3').removeClass('ui-collapsible-heading-collapsed');
$('div').find('.ui-collapsible-content').removeClass('ui-collapsible-content-collapsed').attr('aria-hidden',false);
}else{
$('h3').addClass('ui-collapsible-heading-collapsed');
$('div').find('.ui-collapsible-content').addClass('ui-collapsible-content-collapsed').attr('aria-hidden',true);
}
return false;
}