None.
I can't remember the last time I paid for anything using ANY pennies. Hell, I can't remember the last time I gave anyone CHANGE for anything. 98 times out of 100, I'm using the debit card. 9 times out of 10, I have less than $10 in hard cash in my pocket. If I am spending cash, I never carry any change on me.
Change has just slowly accumulated in our house over the years.