The option to show trailing zeros on your prices has been removed in favor of a filter, as of WooCommerce 2.2x. If you want to hide trailing zeros on your prices, add the following code to your child theme’s functions.php file or via a plugin that allows custom functions to be added, such as the Code snippets plugin. Avoid adding custom code directly to your parent theme’s functions.php file as this will be wiped entirely when you update the theme.
/**
* Trim zeros in price decimals
**/
add_filter( 'woocommerce_price_trim_zeros', '__return_true' );