What is the ruling on evading taxes by paying a gratuity to a tax official, taking into consideration that the imposed tax amounts are considered substantial?

Taxes are of two types: legitimate, from which evasion is not permissible, and oppressive, which are forbidden and from which evasion is permissible, even by paying a bribe, the sin of which falls on the receiver. The work of an accountant follows the ruling on taxes; what is permissible is lawful, and what is forbidden is not permissible due to its assistance in sin. An accountant's defense of someone who legitimately owes tax is not permissible. However, defending someone upon whom an unlawful tax has been imposed carries no blame, even through stratagem and bribery.