Function to limit the number of posts in taxonomy.php

How can I change the post limit for taxonomy.php from that which is defined in the settings page?

Currently I have 10 posts displaying per page, which is fine for the blog part of my site, but I want to show all posts when the user is on taxonomy.php, is there a function that can achieve this?

Use the pre_get_posts hook to check is you are in a taxonomy term archive and change the number of posts ex:

add_action('pre_get_posts', 'change_tax_num_of_posts' );
function change_tax_num_of_posts( $wp_query ) {  
    if( is_tax() && is_main_query()) {
        $wp_query->set('posts_per_page', 5);
    }
}