Round down initial payment price for users switching levels. Useful to make prorated prices look more friendly.

my_pmpro_checkout_level_round_down_initial_payment.php

<?php

// Copy from below here...

/*
 * Round down initial payment price for users switching levels.
 * Useful to make prorated prices look more friendly.
 */
function my_pmpro_checkout_level_round_down_initial_payment( $level ) {
	// We only want to round down prorations.
	if ( ! pmpro_hasMembershipLevel() ) {
		return $level;
	}

	// Round down to an integer.
	$level->initial_payment = floor( $level->initial_payment );

	// Round down to nearest 25.
	$level->initial_payment -= $level->initial_payment % 25;

	return $level;
}
add_action( 'pmpro_checkout_level', 'my_pmpro_checkout_level_round_down_initial_payment', 15, 2 );