Please override the 'formatter' function to achieve this functionality.
$('#nn').numberbox({
formatter:function(value){
var opts= $(this).numberbox('options');
var s = $.fn.numberbox.defaults.formatter.call(this, value);
var idx = s.indexOf(opts.decimalSeparator+'00');
if (idx >= 0){
s = s.substr(0, idx);
}
return s;
}
});