title: Woocommerce coupon rounding issue
body: <p>In our store we enter prices including tax. On frontend we hide decimals (In Sweden we don't really use decimals anymore in prices), but backend we keep them. This is why: <a href="https://krokedil.com/dont-display-prices-with-0-decimals-in-woocommerce/" rel="nofollow noreferrer">https://krokedil.com/dont-display-prices-with-0-decimals-in-woocommerce/</a></p>
  
  <p>We use the function from the link above to hide the decimals on frontend and have also added a function to round off coupons at front end.</p>
  
  <pre><code>/**
   * Trim zeros in price decimals
   **/
   add_filter( 'woocommerce_price_trim_zeros', '__return_true' );
  function iconic_was_loop_position( $position ) {
      return 'woocommerce_after_shop_loop_item_title';
  }
  
  add_filter( 'iconic_was_loop_position', 'iconic_was_loop_position', 10, 1 );
  
  /**
  * Round off decimals for coupons
  **/
  function filter_woocommerce_coupon_get_discount_amount( $discount, 
  $discounting_amount, $cart_item, $single, $instance ) { 
      $discount = ceil( $discount );
      return $discount; 
  }   
  add_filter( 'woocommerce_coupon_get_discount_amount', 
  'filter_woocommerce_coupon_get_discount_amount', 10, 5 );
  </code></pre>
  
  <p>This works well for both prices and percentage coupons/discounts.
  However, say I have a coupon with a fixed cart amount of SEK400, when using it the amount instead changes to SEK402.
  I guess this has to do with how woo applies the coupons combined with the rounding filter.</p>
  
  <p>So my question is, is it possible to exclude the fixed cart coupons from the rounding function in some way?</p>