计算包括银行费用在内的总费用

$surcharge = ($total + ($total * $rate)) * $rate;

$sale = $100
$pct_rate = 0.03; 
$surcharge = $sale * $pct_rate;
$total = $100 + surcharge ; // =103

// test it
$moneyinthehand = 103 - (103 * $rate); // moneyinthehand = $99.91 (which is not $sale price)

$total_in_hand = 100
$bank_cut_pc = 0.03

$to_charge_customer = $total_in_hand / (1.0 - $bank_cut_pc)

>>> 100 / (1.0 - 0.03)
103.09278350515464
>>> 103.09278350515464 - (103.09278350515464 * .03)
100.0

$fee_rate = 3;
$sub_total = 5000;
$surcharge = $sub_total * ($fee_rate / 100);
$total = $sub_total + $surcharge;