posta, для checked лучше prop
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<script src="http://code.jquery.com/jquery-1.9.1.js">
</script>
<script>
$(document).ready(function(){
$('#reg-selectall').on("click", function(){
$("label input").prop('checked',true);
})
$('#reg-deselectall').on("click", function(){
$("label input").prop('checked',false);
})
});
</script>
</head>
<body>
<button id="reg-selectall">Выделить все</button>
<button id="reg-deselectall">Снять все</button>
<label><input checked type="checkbox" name="one">1</label>
<label><input checked type="checkbox" name="two">2</label>
<label><input checked type="checkbox" name="three">3</label>
</body>
</html>