Is it permissible to sell Roman treasure unearthed in Tunisia on the black market and pay Zakat on it, knowing that Tunisian law grants the extractor of the treasure only 5% of its value?

If a Muslim finds a rikāz (pre-Islamic treasure) in barren land or a ruin, they must pay one-fifth (20%) of it and distribute it among the beneficiaries of zakāt. What remains after extracting the one-fifth belongs to the finder, and they may personally distribute this one-fifth to the poor and needy without needing to hand it over to the ruler. There is no difference whether the treasure is gold, silver, jewelry, or iron, whether it is little or much, and the passing of a year (ḥawl) is not a condition for it. As soon as it is found, one-fifth of it is to be extracted, and the remainder becomes due, based on the saying of the Prophet, peace and blessings be upon him: "And for rikāz, there is one-fifth."