The latest version (17.6.61) contains new filter spell_out_rupees
So you can do:
{{ total.number | spell_out_rupees }}
I might actually remove this filter and inject this as a custom field if currency is set to Rupees. This is because if this must be shown (legal requirement), all users with Rupees would get this as default without using custom template.
For now it’s just a filter for testing purposes.