Reddit, I just quit a job where the owner is running the business illegally. What do I do now?

Throwaway for pretty obvious reasons.

A little background...

I dated a guy from April-November of 2011. I was super close with his entire family, and pretty much regarded them as my second family. When we broke up, I still wanted to remain close with his family, including his parents and siblings. His family goes on vacations twice a year typically, in the summer and in the winter time. In December, his family planned their Christmas trip, and as it turns out, his mom didn't plan as much ahead as she should have and didn't have anyone to help run her business while they were away.

Cue my entrance into this business. She asked if I would mind learning the ropes for a bit before they went away, and if I would be comfortable working in a retail setting while her and her family were away. I said of course. I had never worked in retail previous to this, so I was a little intimidated at the thought of it, but I wanted to show that I still cared about their family and I wanted to prove that I was trustworthy and a good worker.

Anyway...

On my first day of training, she shows me the basics and how to use the "cash register" which consists of a drawer where cash goes, along with a credit card swipe pinpad sort of deal (but I don't actually know what they're called), and a computer with a program in which we enter the price for certain clothing items and save the information on purchases. These three items run individually, that is, the credit card swipe doesn't save information in the computer, the drawer isn't hooked up to the computer or the swipe, etc. The cash drawer is literally the same thing as a drawer on a desk. Inventory isn't saved on the computer in any way. When someone purchases clothing, we click on "sell miscellaneous item" or something to that effect and manually put a price on what we're selling. At the end of the purchase, we take cash (and give change) or swipe the credit card (enter the amount on the pinpad, get a signature on the receipt, and put the receipt under the corner of the computer) and add up the total at the end of the day.

Red flag #1 came up when I was told to not put cash purchases in the computer at all. When someone pays in cash, I was told to simply put the cash in the drawer, give change, and delete the entry in the computer before saving the information. This way, the cash purchases don't show up on the "end of day" total. My ex's mom, therefore, doesn't have to pay extra taxes on cash purchases.

Red flag #2 came up when I was told I was going to be paid under the table. I didn't sign any form before working there, there was no W-2 or W-4, and I therefore don't have to pay taxes on the money that I made there. Neither does she.

Red flag #3 came up when I realized that we don't write receipts for cash purchases, only credit cards. And those receipts don't have individual items on them, but just the total for the purchase (for example, if somebody bought item #1 and item #2, it wouldn't list the items and their prices separately, but the total of #1 and #2 together).

The red flags made me feel uneasy about everything that was going on in that store. But I figured I'd only help out for that week or two, and then be done. It wasn't until February of 2012 that I started being put on the schedule more and more. I ended up being an on-call sort of person. If someone needed their shift covered, I was called to see if I could fill in. I became a more regular worker, but the red flags kept making me feel uneasy about everything.

I have since grown apart from the family that owns the shop, but I had been scheduled relatively regularly, all the while feeling really weird about everything. Finally, about a week ago, I wrote a letter of resignation and formally quit because I figured if she got caught, I wasn't going to be caught up in all the mess. I'm in the middle of my two weeks, and will be working there tomorrow morning.

Reddit... what do I do? Knowing all of this really shady stuff is going on at a store that I used to work at and that is run by my ex's family? Do I report her? How would I go about doing that? Do I forget about it and move on?

TL;DR: Worked for a store run by a family that I used to be close with. Turns out, everything that seems mildly important is being handled illegally (being paid under the table, no contracts, taxes not being paid on cash purchases, no receipts, etc.). I recently quit. What do I do now?