Capt_Zoolander - the bonus scheme you speak of is true of a number of APAC countries, but not OZ. Too many checks and balances in place here which means any such payments quickly draw the attention of the auditors and internals affairs.
Here I have heard of instances in the ATO of the reverse occurring - tax officers hinting for "favours" to let people off - but this has been for very small fry - not real tax evasion stuff. Again - too many checks and balances.
In some Asian countries this practise is rife and is officially included as part of the "salary package" - "commissions" of up to 25% depending on the amount collected!!!