I don't think tax evasion is possible in any developed country.
What are you going to do say when the bank sees you keep receiving money out of nowhere?
The only way would be to never leave the Bitcoin ecosystem, simple as that. Get paid in BTC, buy in BTC.
If you need fiat, i guess the best way is still Localbitcoins IRL transaction.
that's why you use services that buy thing for you directly in bitcoin, like all4btc or
https://xmr.to/ for monero
other may find more comfortable to use anon card, with a limited amount, i guess it could work, yet the most anon way remain cash to bitcoin, to avoid taxation