Randomizing Based On Criteria

I have created a db where I need to run a report based on randomizing. Basically there is a table ORDERS that is updated daily with orders from clients.

Table structure is:
ORDER ID (autonumber).
CLIENT.
ORDER.
Quantity,
Date.

Sampling criteria is:
if number of Orders is from:
1-10 show me 90% of them
11-20 show me 85 % of them
21-100 show me 51% of them etc

I did found this code for the randomizing with autonumber:

Private Sub cmdSelect_Click()
Dim SQL As String
Dim sWhere As String
Dim iCount As Integer
Dim i As Integer
Dim j As Integer
Dim iSelectHowMany As Integer

[Code] ...

How to integrate into this code my sampling?