I think the value of pennies to the economy is negative.

Every time I have to handle a penny it wastes my time and energy for no gain. I never find having a penny useful unless it will prevent me from getting more pennies. Multiply that by everyone in the country and that is quite a waste of time (i.e. money). There would be almost no loss of economic efficiency if we get rid of pennies but a nice savings in real time and energy, to say nothing of the waste that mining, refining, stamping and distributing them costs.