I have checked Magento 2.2.3 by default showing up 4 decimal places on selling price in catalog product grid and frontend side layered navigation except for price attribute other than showing up 4 decimal places. Is that magento2 default issues?
If you like my question is useful then kudos on it.
By default Magento 2 showing two digits.
Maybe you are using other locale and it will use 4 digit, may i know your locale?
Price showing up correct but other attribute created based on price like the special price they will display 4 decimal places in product grid admin backend