Does Kliently handle tax on invoices?

Yes. You can add tax per line or per invoice, alongside discounts, and the totals update live as you make changes. Per-line tax is there for the cases where one item is taxable and another isn't; per-invoice tax handles the common case of a single rate on the whole bill.

Kliently calculates the totals for you, but it doesn't decide your tax rates or obligations — you set the rate that's correct for your situation and jurisdiction, and the live totals show exactly what the client will see.