Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$249.29	12.455%	$280.3391	$280.34	$280.35	$280.30
Purchase #2	$241.45	13.283%	$273.5218	$273.52	$273.50	$273.50
Purchase #3	$55.39	7.258%	$59.4102	$59.41	$59.40	$59.40
Purchase #4	$244.30	13.621%	$277.5761	$277.58	$277.60	$277.60
Purchase #5	$164.47	7.167%	$176.2576	$176.26	$176.25	$176.30
Purchase #6	$20.40	7.631%	$21.9567	$21.96	$21.95	$22.00
Purchase #7	$80.86	3.285%	$83.5163	$83.52	$83.50	$83.50
7 purchase totals =	$1,056.16		$1,172.5778	$1,172.59	$1,172.55	$1,172.60