Is it permissible, from a Sharia perspective, for the buyer to attest in the land sale documents that the price is less than 90,000 Algerian Dinars, knowing that the intention behind this is to reduce the 5% tax allocated to the tax authorities?

If the taxes levied on land are illegitimate, it is permissible to use stratagem to completely eliminate them or reduce them, because they are an injustice. Scholars have permitted the oppressed person to repel injustice by means of lying or similar methods if they find no other way. However, if the taxes are legitimate, it is not permissible to use stratagem against them.