I work in finance at a car dealership so I think I can help.
The answer is it depends..
There are a few lenders that will accept 3 months of bank statement deposits as proof of income. Santander is an international company that is one of those lenders.
Other lenders will accept the bank statements but still require a signed 4506-T form to verify the income as claimed with the federal government (capital one is one of those)
Your best hope is to get income stipulations waived (I imagine the dealer would have if they could already) which means your credit isn't strong enough to do so.
You are doing the right thing by depositing your money in to your account so there is atleast some type of paper trail for your tips.
Seek out a friendly knowledgable secondary finance person (they exist I swear) and let him know your income dillemma up front. You can calculate your income by average the deposits from 3 months worth of bank statements.
Just fyi when it comes to proving Non-W2 wages via tax returns the income is calculated off of line 31 on your schedule C's which is a net profit/loss. The problem there is that the likelyhood that you claimed enough of your tips to put you over the minimum income threshold is almost nill. This is also a problem if you've been with your employer for less than 2 years.
Remember when buying a car that cash is king... Some lenders (santander in particular) will waive income stipulations at dealership request if you 30% of the cash price down up front.
Plus there is social contacts. I don't mean the FB, Twitter, etc. I mean talking to someone. You say you deposit all your money to your bank. What bank do you use, is there a loan officer there? Before I had my CR cleaned up, I had a LO at my local bank that would try everything she could to get me into a loan or make me a better deal. She still calls and asks if there's anything I need or anything she can do.
Whenever I go into the bank, everyone calls me by name, asks how me and the family are doing. The branch manager always takes the time to come over and see and talk to me. They have little gifts and customer appreciation things they give to customers, like a few dollars in quarters to wash your car, candles, "geared more for the DW on that one", but just little things they offer to show appreciation.
Sometimes in the world of computers and everything online, the personal connection is lost. You are a score, a number, I kind of like the interpersonal connection myself. Just wanted to throw that out there. Good luck!