Starbucks Cashier

I walked up to the Starbucks cashier. I didn't really want to buy a coffee, but I was in the Starbucks and I needed to waste some time, and well, what else is there to do in a Starbucks? Needless to say, I was unprepared.
"Uhhh..." I said. "Hmmm..."
Why not get the ol' standby? What the fuck, why not?
"I'll have...(each syllable drawn out in an obnoxious tone)...a grande soy latte."
I began to count my money. I had no change; bills would have to do.
The cashier punched the order into his register.
"$4.01."
"$4.01?!"
I looked at my bills. One goddamn penny. If he gave me a couple seconds, I could probably find one on the floor somewhere, but still. I was bemoaning my decision already, staring at my bills as if that one goddamn penny would suddenly manifest itself.
The clerk obviously caught on to my restlessness. Perhaps he thought I was having trouble counting, or that I was one dollar short. Next thing I knew, he started punching something else into his register.
"$2.85."
I looked up at him. He stared back at me. Not smiling, not frowning; a deadpan stare.
"Uhhh..." I said, looking down at my bills again, still trying to process what had just happened. "So it's not...$4.01."
Deadpan stare.
"$2.85."
"Is it $4.01 or $2.85?!"
"I gave you a discount, so now it's $2.85."
I looked at him. He looked at me.
"Is there a...reason for said discount?" I asked slowly, perhaps with the anticipation of a punchline.
"Does there...need to be one?" said the cashier with his deadpan stare.
"No..." I said.
I gave him the money. He gave me my change.

If he had perhaps smiled once during the whole interaction, maybe I would have chalked this one up as him trying to flirt with me, though no such thing has ever happened before. But all I can think of is his deadpan stare.

No idea.