Can't find give_donation_total

Am trying to amend give total donations, I saw this:
$total = apply_filters( 'give_donation_total', $_POST['give_total'] );
but so far I have searched in the whole plugin, I can’t find where the give_donation_total filter is declared or added.
In fact, commenting this out still works so am wondering what’s is it actual use there.

https://www.ads-software.com/plugins/give/