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	$140.31	4.609%	$146.7769	$146.78	$146.80	$146.80
Purchase #2	$29.71	7.422%	$31.9151	$31.92	$31.90	$31.90
Purchase #3	$230.67	7.576%	$248.1456	$248.15	$248.15	$248.10
Purchase #4	$205.87	8.723%	$223.828	$223.83	$223.85	$223.80
Purchase #5	$48.56	12.634%	$54.6951	$54.70	$54.70	$54.70
Purchase #6	$138.63	8.561%	$150.4981	$150.50	$150.50	$150.50
Purchase #7	$226.82	6.667%	$241.9421	$241.94	$241.95	$241.90
7 purchase totals =	$1,020.57		$1,097.8009	$1,097.82	$1,097.85	$1,097.70