we wish to round all prices decimals, for example, $3.22 > $3 and $3.59 > $4. Not only on display price but also the calculation during checkout.

We found a really good solution from:
How to round WooCommerce product prices to the tens digit place?

and modify the code to be:

add_filter( 'raw_woocommerce_price', 'round_price_product', 1000, 1 );
add_filter( 'woocommerce_product_get_price', 'round_price_product', 1000, 1 );
add_filter( 'woocommerce_product_variation_get_price', 'round_price_product', 1000, 1 );
function round_price_product( $price ){
    // Return rounded price
    return round( $price);
}  

It works well in front end. All prices are integer now, and calculation is correct. However, it crushes down the backend product list page. And of course we cannot create/edit products too.

Any idea? Any input is appreciated.