Problema nu e la intval, ci la inmultire. Explicatia pe larg, direct din manual, floating point numbers:
[…] rational numbers that are exactly representable as floating point numbers in base 10, like 0.1 or 0.7, do not have an exact representation as floating point numbers in base 2, which is used internally, no matter the size of the mantissa. Hence, they cannot be converted into their internal binary counterparts without a small loss of precision. This can lead to confusing results: for example, floor((0.1+0.7)*10) will usually return 7 instead of the expected 8, since the internal representation will be something like 7.9999999999999991118…
So never trust floating number results to the last digit, and do not compare floating point numbers directly for equality.
Ca o paranteza, nu folositi niciodata operatorii aritmetici atunci cand lucrati cu valori numerice importante, gen bani. Folositi extensia BC Math. E cam peste mana sa scrii bcmul($val, 100) in loc de $val * 100, dar asta e situatia.
Cu singura diferenta ca in Python ai mai putine sanse sa te lovesti de ea. Bine, asta pana vrei sa lucrezi cu JSON: http://stackoverflow.com/questions/1447287/format-floats-with-standard-json-module (PS: al doilea raspuns e bun aici, nu primul care e un hack destul de tricky, caruia trebuie sa ii faci revert dupa ce l-ai folosit)