Third, it is very unlikely that prices would be rounded up, since such rounding would not carry through to the cash register after sales taxes are applied, and retailers would lose the perceived marketing benefit of posting a price that ends in 9 cents.
In the absence of a penny, rounding would only need come into play in cash transactions and would apply to the total bill after tax, and not to each individual item purchased. If applied symmetrically,  1  Varya Taylor. “Trends in Retail Payments and Insights from Public Survey Results.” Bank of Canada Review. (Spring 2006): 25-36.