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	$248.98	10.118%	$274.1718	$274.17	$274.15	$274.20
Purchase #2	$42.71	3.694%	$44.2877	$44.29	$44.30	$44.30
Purchase #3	$26.51	11.794%	$29.6366	$29.64	$29.65	$29.60
Purchase #4	$179.94	5.786%	$190.3513	$190.35	$190.35	$190.40
Purchase #5	$136.25	5.271%	$143.4317	$143.43	$143.45	$143.40
Purchase #6	$132.47	9.181%	$144.6321	$144.63	$144.65	$144.60
Purchase #7	$171.72	3.103%	$177.0485	$177.05	$177.05	$177.00
7 purchase totals =	$938.58		$1,003.5597	$1,003.56	$1,003.60	$1,003.50