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	$134.71	8.830%	$146.6049	$146.60	$146.60	$146.60
Purchase #2	$124.25	5.629%	$131.244	$131.24	$131.25	$131.20
Purchase #3	$228.94	9.765%	$251.296	$251.30	$251.30	$251.30
Purchase #4	$54.80	9.724%	$60.1288	$60.13	$60.15	$60.10
Purchase #5	$138.36	3.547%	$143.2676	$143.27	$143.25	$143.30
Purchase #6	$217.88	13.414%	$247.1064	$247.11	$247.10	$247.10
Purchase #7	$82.46	10.159%	$90.8371	$90.84	$90.85	$90.80
7 purchase totals =	$981.40		$1,070.4848	$1,070.49	$1,070.50	$1,070.40