Enable the following codes by entering them at the 'Press Start' screen. If the codes have been entered correctly you will hear a confirmation sound.

Unlock Level Select:
Press X(2), Z(2), Y(2), Z, X, Y(2), X, Z.

Unlock Extra Money:
Press Y, X, Z, Y, X, Z, X(2), Y, Z, X, Y.

Increase Reputation:
Press Y(2), Z, X(2), Z, Y(3), X(3).

Good Reputation
At the Press Start screen enter the following code to gain a good
reputation:
Y, Y, Z, X, X, Z, Y, Y, Y, X, X, X.

More Money
At the Press Start screen enter the following code to get some easy money:
Y, X, Z, Y, X, Z, X, X, Y, Z, X, Y.

Unlock Level Select
At the Press Start screen enter the following code to unlock Level Select,
if the code has been entered correctly a sound will confirm:
X, X, Z, Z, Y, Y, Z, X, Y, Y, X, Z.