Using round() to get exact value - PHP

Question

Hey guy's I am working on a project of mine which involves the use of money. I am trying to not use round anymore because, it's rounding things to nearest tenth and I need exact numbers. One reason I was using it, was because it was giving a whole number.

The way I am working my number system is that 100 = $1, 2000 = $20, etc.. I was currently using the round function because it would get rid of the decimal point for me and give me a whole number, lets say: 223 which in turn would = $2.23 .

Here is what I am using:

$amount += round(($amount / 29) + 30);

Here are the numbers:

Lets say we have a charge of 100 and we add 125 which equal 225 (USD $2.25) . Now we add taxes and processing: + 2.9% + $.30 . After multiplying 2.25 by 2.9% and adding .30 the amount would be: 0.36525 - this is the amount that should be added than to the $2.25 which than would be 261 = $2.61

The issue is because of the rounding, when I look in my Stripe panel (I am using Stripe API for payments) I see a charge of $2.63 . So my question is, how would I go about making it exact without having any rounding and decimal places.

UPDATE:

Here is the above example more explained:

Lets say we have a charge of 100 and we add 125 which equal 225 (USD $2.25) . Now we add taxes and processing: + 2.9% + $.30 . After multiplying 2.25 by 2.9% and adding .30 the amount would be: 0.36525 - this is the amount that should be added than to the $2.25 which than would be 261 = $2.61

So now with that the actual value of amount that should be charged is $2.61 but instead when using the round it gives me 263 which also means $2.63 . The above example is the simple math that is correct.

Answer 1

In order to avoid calculation hiccups like that, only round the final result. Keep all other calculations as accurate as possible:

$original = 100;
$original += 125;

$tax = $original * 2.9 / 100; //+2.9%
$tax += 30; //+$.30

$original += $tax; //Add tax.

echo $original; //Result is 261.525. Round as you please.

Answer 2

You can specify precision and rounding method to keep it consistent ( PHP round() ), then you can deal with the actual values. Doing math tricks like multiplication by a multiple of 10 will only make it more confusing in the long run.

$amount += round(($amount / 29) + 30, 2, PHP_ROUND_HALF_UP);

Will this solve your problem?