eiru_nutty_bavarian_invoice/template.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <template id="indexs" inherit_id='point_of_sale.index' name="POS Header">
            <xpath expr="//link[@id='pos-stylesheet']" position="after">
                <link rel="stylesheet" href="/eiru_nutty_bavarian_invoice/static/src/css/pos.css" />
            </xpath>
        </template>
    </data>
</openerp>