You're only toggling the div for the link that was clicked, what you need to do is not only show the div you want but hide the others. Lots of ways to do this, but one is to mark the divs you want to be a part of the toggling so you can target them to be hidden.
<script type="text/javascript">
function ShowOrHidePanel(div_id)
{
$("[data-type='toggleDiv']").hide();
$("#" + div_id.id).show();
}
</script>
<div id = "div_1" data-type="toggleDiv">Div 1</div>
<div id = "div_2" data-type="toggleDiv">Div 2</div>
<div id = "div_3" data-type="toggleDiv">Div 3</div>