Unit price more decimal digits

HI, can anybody help me to set up my store to have 4 decimal digits for unit price?

Some of my products are so cheap I need to use 4 decimal digits. I tried to set it up in Admin-> Currencies, but it only display in cart and during the checkout. Once customer is redirected to PayPal website it shows up total amount based on qty x unit price rounded to 2 digits.

The best would be to show unit price with 2 decimals if product has got a price with 2 decimals only, and if product unit price is with 3 or 4 decimals, then show unit price with 4 decimals. It can be done with some if condition I think, but where to place it and what exactly. at the end of checkout the total amount can be rounded to 2 decimals so it’s going to work with PayPal.

Thank you for your help and hope this can be figured out