floats are not supposed to be exact (per definition). do not use them on currencies. calculate cents ant use (agein) number_format() to display them prooperly. No bug in PHP, bogus.

what type should i do for currencies, so?

ok. let's don't call it a bug...
let's call it for example a little magic of floats.

but don't u think u could correct it?

lets call it what it is: an inevitable rounding error
that occurs when converting floating point values from
internal binary to human readable decimal format

use integers and count cents instead of dolars
or use http://php.net/number_format for output
as already suggested

by the way: the result is 56.999999..., not 
57.999999..., so you are off by 0.000.....1
not 0.99999..... which is not so bad after 
all

thanks very much for explaining. i haven't link teory with practice (about floats). probably i realy work too much. :)

let me ask one more question:
if i store prices in postgresql as numeric(10,2), how can i secure handle it in php?
could i do: 
$price_c = (int)($psql_num_price * 100); //?
and how to write it back?
$psql_num_price = $price_c / 100; //?

thanks one more time.