Is there another way to enable taxes accountability in odoo?

So I have this problem where I need to make sure taxes are accounted for in odoo.
My particular problem is not handled by odoo taxation procedures as far as I know.

This is the process.

I have a product say petrol being sold from a custom module I have created in odoo. The way these kinds of petroleum products are sold to be exact is that only a percentage of that product is vatable say 50%. The rest is non-vatable and goes to the government. Taxes are already included in the price.

Now here comes the fuzzy part.

Considering that these products are sold anonymously.(anonymously in the sense that a stranger just fuels their vehicle without the agents recording who or what product they just fuelled. The fuel stations just record the number of litres sold in a day and move on).

So with this, I created an invoice that is in no way tied to the product, (This is possible in odoo) as they wanted, but now I am stuck on how to account for the taxes for every sale created in my custom module where these products are being sold.

I know this is a lot of reading, but I would really appreciate any ideas on how to go about this or even a solution.

Thank you in advance.