pos/pos_customer_display/pos_customer_display.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <template id="assets_backend" name="point_of_sale assets2" inherit_id="web.assets_backend">
            <xpath expr="." position="inside">
                <script type="text/javascript" src="/pos_customer_display/static/src/js/customer_display.js"></script>
            </xpath>
        </template>
        <template id="index" name="pos_customer_display index" inherit_id="point_of_sale.index">
            <xpath expr="//link[@id='pos-stylesheet']" position="after">
                <link rel="stylesheet" href="/pos_customer_display/static/src/css/pos_customer_display.css" id="pos_customer_display-stylesheet"/>
            </xpath>
        </template>
    </data>
</openerp>