To laugh all the way to the bank means to be happy about the money earned, even if it was earned in a way that others might think is unfair which is what the speaker did as he exploited the city's resources.
Consider the statement "I would exploit the city's resources for all I could get and then be very pleased with myself as I deposited the money earned through unfair means.". Is the statement "I would twist the city's tit for all I could get and then laugh all the way to the bank." false? Yes/no/unknown