It's under the "THIS GAME IS PROVABLY FAIR!" tab right at the top of the page.
Two strings are created :
STRING1 = "[NONCE]:[SERVER SEED]:[NONCE]"
STRING2 = "[NONCE]:[CLIENT SEED]:[NONCE]"
Then HMAC-SHA512 is used to hash STRING1 with STRING2 as the secret key, giving us a 128 character hex string.
The first 8 characters of the hex string are taken and converted to a decimal.
This decimal is then divided by 429496.7295 and rounded off to the nearest whole number.
This whole number is used as your roll, with the maximum possible value being 10,000.
The payout table also states that possible results are 0-10000, not 1-10000 so both results 00000 and 10000 have half the chance of being rolled than any other number due to rounding.
It's free to play so I don't see any grounds for complaint that people being scammed by this.