Odoo-Build/snippets/account.report_invoice_document.round_quantity.xml

<?xml version="1.0"?>
<data inherit_id="account.report_invoice_document" priority="50">
    <xpath expr="//span[@t-field='line.quantity']" position="replace">
        <span t-esc="'%.2f' % line.quantity"/>
    </xpath>
</data>