If you simply round to the nearest penny (3,4,5,6,7=5, and 8,9,0,1,2=0)on all transactions, then it evens out.
Those pennies really don't add up. See if you can find a store that won't add in the extra pennies to round you up, seriously - they certainly don't care.
The IRS generally allows rounding to the nearest dollar on tax forms (at least individual and small business; not sure if large corporate are allowed to round even more). In fact, all the common tax software does so automatically; the only way to file a return to the cent is to do so by hand.
A lot of fraud has been perpetuated by people shaving fractions of pennies off payrolls etc. Of course it adds up, and nobody's going to be rounding down anything. If a product costs 1.37, you will pay 1.37 with a credit card, and 1.40 with cash. And yeah it's the blue collar slob with two bankruptcies whose going to get his pennies shaved off.
No you won't. I never see charges with fractions of pennies when I use my card at the gas pumps (which charge 9/10¢ extra per gallon, remember); why would I see charges with fractions of nickels when pennies are gone?
Those pennies really don't add up. See if you can find a store that won't add in the extra pennies to round you up, seriously - they certainly don't care.