Paying 'taxes' on all your income is an abstraction - the same abstraction that allows runners to keep all their money if their fake SIN gets burned, instead of their bank accounts being frozen.
While I support enjoying the game without taking things to an unplayable extreme (albeit at times curious as to what constitutes an unplayable extreme), it's not difficult to burn accounts attached to SINs without it being excessive. Have players keep certified credsticks, and only use SIN accounts to hold money that has to be there. (for whatever reasons, if any)
It's not like "normal" people don't use credsticks anyways. A legal person uses credsticks to probably pay for pretty much everything, if they need more, they go to their back account and reload their credstick. Unless they get payed exclusively in scrip, credsticks are basically the universal credit card that doesn't charge interest; it's convenient, portable, and accepted almost everywhere. I would reason then that someone with a Fake SIN can pass as an entirely legal person without having a banking account, just using credsticks. This does bring up an interesting dilemna, because if someone probes deeper into their history, where are they getting their credsticks funded? Not from a bank account usually.
Kind of does bring up an issue though, since credsticks in SR5 are entirely unhackable, you could just have a "legal" credstick set up with just enough money to pay rent etc, which would be the only credstick that the taxman would see. If you have a Low Lifestyle, that is equivalent to about 2,000 nuyen a month, give or take, and I just don't see how a taxman would know about your other credsticks unless he physically had all of them in his hands (which, let's be honest, as a Shadowrunner that's a bad idea). However, maybe that is getting a little too theoretical and realistic. At some point, you have to step back and say, "The rules are there for a reason, it's a negative Quality for a reason, let's either just follow them or come up with an acceptable compromise with my GM."