将 PHP 中的最后一位四舍五入为 0、5 或 9

Question

I am looking to round the last digit of product prices in WooCommerce with a PHP function, based on 3 rules. Price has to include cents and it does not matter if it gets rounded up or down.

If end between 0 and 4, change to 0

If end in 5, no change and stays at 5

If end between 6 and 9, change to 9

For example:

A price of $23.12 will be rounded to $23.10

A price of 39.45 will be rounded to $39.45

A price of $4.26 will be rounded to $4.29

Currently using the following code but it only rounds to a whole number.

function my_rounding_function( $price ) {
    $price = round( $price ); 
    return $price;
}

Any help would be very much appreciated: :)

Answer 1

Try this. Using the BC math functions, this will guard against rounding errors. Updated to truncate (round) thousands first.

Outputs:

float(1)
float(1)
float(125.99)
float(12.3)
float(2.05)
float(3.69)

Code:

<?php

function roundPerceptual(float $price):float
{
    // Truncate to precision of 2 decimals.
    $price = round($price, 2);

    // Get last digit using MOD 10.
    $lastDigit = bcmod($price * 100, 10);

    // + casts the string to a number, compare to each threshold.
    if (+$lastDigit < 5)
        $newDigit = '0';
    elseif (+$lastDigit > 5)
        $newDigit = '9';
    else
        // Equal to 5.
        $newDigit = '5';
        
    // First drop the old hundredth, then add the new hundredth.
    // Again, use + to cast to float.
    return ($price - +"0.0$lastDigit") + +"0.0$newDigit";
}

$prices = [ 1, 1.04, 125.959, 12.337, 2.05, 3.67 ];

foreach ($prices as $price)
    var_dump(roundPerceptual($price));
/*
Outputs:
float(1)
float(1)
float(125.99)
float(12.3)
float(2.05)
float(3.69)
*/

Answer 2

function my_rounding_function( $price ) {
    $price = (string) $price;
    if(strpos($price, '.'))
    {
        if($price[-1] < 5)
        {
            $price[-1] = 0;
        }
        elseif($price[-1] > 5)
        {
            $price[-1] = 9;
        }
    }
    return (float) $price;
}

echo my_rounding_function(15) . '<br>';
echo my_rounding_function(15.3) . '<br>';
echo my_rounding_function(15.5) . '<br>';
echo my_rounding_function(15.8) . '<br>';
echo my_rounding_function(15.43) . '<br>';
echo my_rounding_function(12.45) . '<br>';
echo my_rounding_function(12.47) . '<br>';

// output

// 15
// 15
// 15.5
// 15.9
// 15.4
// 12.45
// 12.49