they are integer, whole numbers, not fractions.
This is why you don't understand. They are displayed as whole numbers but are calculated from decimals.
From the provably fair information on the site:
How are rolls calculated?
1 Two strings are created :
STRING1 = "[NONCE]:[SERVER SEED]:[NONCE]"
STRING2 = "[NONCE]:[CLIENT SEED]:[NONCE]"
For your last roll :
STRING1 = "187642:dd2d1349d29ccb2b154633ffe1083fab798480781a2ae5f85d302e21731aad22:187642"
STRING2 = "187642:vXqTuIUiZsRsIqSW:187642"
2 Then HMAC-SHA512 is used to hash STRING1 with STRING2 as the secret key, giving us a 128 character hex string.
3 The first 8 characters of the hex string are taken and converted to a decimal.
4 This decimal is then divided by 429496.7295 and rounded off to the nearest whole number.
5 This whole number is used as your roll, with the maximum possible value being 10,000.
The part I bolded explains where the decimal is introduced and that in turn when rounding up will reduce the chance to 20,000:1.
Over in the thread on the Micro Earnings board, someone kindly wrote a little C++ program to work it out.
https://bitcointalk.org/index.php?topic=319540.msg25099985#msg25099985