Where's the cambio?

I don't know why I ask because the answer's always the same. Here's a typical scenario:

Me: (expectantly) Tienes cambio? (Do you have change?)

Vendor: (programmed response) No tengo cambio. (I don't have change.)

Whenever I try to use a large bill, the standard response is, "No tengo cambio." And I'm not really talking about big bills like a $50USD or $100USD, I'm talking about bills that are worth less than $10. So here's what I've noticed: 100 or 200 peso bills ($7.50 and $15, respectively) are not gladly accepted, sometimes a 50 peso bills ($3.70) is frowned upon, and don't even try using a 500 peso bill ($37.80). 

Allow me to contextualize the dilemma so many of us face:

• I went to the dentist (400 pesos), but when I tried to pay with a 500 peso bill (reasonable enough, right?), the secretary wouldn't take it.
• A man steps on the bus (3 pesos) and tries to pay with a 50 peso bill. He was rejected at first, but when he had nothing else, the driver surprisingly came up with change.
• I go to the market and buy a bag of clams (70 pesos). I pull out a 200 peso bill, and the man says to me, "I know you have something smaller. (Points to my wallet) Right there."

So, basically, in an effort to keep small change, people lie about not having any. Change is what everyone wants and needs--change for the bus, change for the market, change for the small shopkeepers. But what I have are large bills because that's what the ATM shoots out. In this country, the ATM should be spitting out coins like a slots machine! It's change we all want!! 

Anyway, I'm used to being lied to about change because I'm learning to see it as more of a survival methodology than a lie. Though, in all respects, a lie IS a lie. This is what I wondered today as I saw someone fall victim to "no tengo cambio": if I were a shopkeeper or bus driver, would I, too, engage in this game of lies? Would you?