Hi,

You can inherit document_tax_totals template like following.

<template id="report_sales_total_inherited" inherit_id="account.document_tax_totals">

    Add your custom code using xpath

</template>

Or

You can call a new template in the invoice report with the same code as document_tax_totals.

template id of invoice report is account.report_invoice_document

For more reference you can check the blog below.

https://www.cybrosys.com/blog/inheriting-existing-pdf-reports-in-odoo14

Regards