How to fix the price in hryvnias in Opencart with the main currency $ (regardless of the exchange rate)?

Question

opencart

There is an online store, the main currency is the dollar $ (for accounting and pricing), in the client part the price is displayed in hryvnia at the rate (set manually, often changes)
But! It is necessary to fix the retail price in UAH. That is:
"Product 1" at the rate of "25.0000" costs "1000 UAH ($40)"
Here the rate changes, for example it becomes "28.57". And I need the product not to change the price by UAH 1143 (40 * 28.57 = 1142.8
)
solutions are ready, can someone tell me which way to look
There is another nuance: each product has only 4 prices (retail/opt1/opt2/opt3) and you need to fix only the retail, and the rest to be considered according to the standard formula
Thank you all in advance