Format the amount in Easy Digital Downloads to remove the decimal points, but only if the number is a whole number.

gistfile1.php

<?php

function my_child_theme_edd_format_amount_decimals( $decimals, $amount ) {

	if( floor( $amount ) == $amount )
		$decimals = 0;

	return $decimals;
}
add_filter( 'edd_format_amount_decimals', 'my_child_theme_edd_format_amount_decimals', 10, 2 );