in magento 1.x for price roud i used extension https://github.com/openstream/Magento5CentRounding Does have somebody any solution for magento 2, or which functions i need rewrite ?
For round the price on checkout page you need to extend
for rounding grandtotal or base grandtotal in your grand.php (which you have extend) in collect method.
Using preference you can do this easily. Let me know if you need further assistance. Thank you