The Romajinator was tool I made for converting Japanese Katakana into romaji, i.e., roman characters. I’ve recently updated it so that it can also convert Hiragana into romaji. Any serious student of Japanese will have no more problems reading hiragana or katakana than a student of Chinese would have reading pinyin.
It’s mostly just for fun, but for people living in China or other countries in Asia, it might be useful.
さむらい -> samurai にんじゃ -> ninja いちご -> ichigo -> strawberry いぬ -> inu -> dog
In general, romaji vowels are pronounced fairly similarly to pinyin vowels. The big exception is the “e”, which sounds a bit closer to a “short e” in English. The “o” sounds somewhat like an English “long o”. Vowels with a macron bar over them are voiced for a longer period of time. Doubled consonants represent a pause before the consonant. For example “kippu” would sound like “key”, followed by a pause, and then “poo”.
The above is obviously a very rough explanation. For a more pronunciation guide, I recommend the Wikimedia Commons: Japanese pronunciation page.