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	$151.87	12.325%	$170.588	$170.59	$170.60	$170.60
Purchase #2	$135.83	6.227%	$144.2881	$144.29	$144.30	$144.30
Purchase #3	$16.44	12.107%	$18.4304	$18.43	$18.45	$18.40
Purchase #4	$242.43	9.627%	$265.7687	$265.77	$265.75	$265.80
Purchase #5	$204.29	12.159%	$229.1296	$229.13	$229.15	$229.10
Purchase #6	$172.35	6.263%	$183.1443	$183.14	$183.15	$183.10
Purchase #7	$159.61	12.726%	$179.922	$179.92	$179.90	$179.90
7 purchase totals =	$1,082.82		$1,191.2711	$1,191.27	$1,191.30	$1,191.20