Hi,

To change the label from "Total" to "Gross" you can create a new template that extends the original one.

Use the following code to change the label:

<?xml version="1.0" encoding="UTF-8"?>
<odoo>
<template id="custom_tax_totals_field" inherit_id="account.TaxTotalsField">
<xpath expr="//label[@class='o_form_label o_tax_total_label'][last()]" position="replace">
<label class="o_form_label o_tax_total_label">Gross</label>
        </xpath>
    </template>
</odoo>

Regards