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	$129.85	7.297%	$139.3252	$139.33	$139.35	$139.30
Purchase #2	$131.57	11.472%	$146.6637	$146.66	$146.65	$146.70
Purchase #3	$68.41	3.471%	$70.7845	$70.78	$70.80	$70.80
Purchase #4	$127.65	3.148%	$131.6684	$131.67	$131.65	$131.70
Purchase #5	$59.32	8.297%	$64.2418	$64.24	$64.25	$64.20
Purchase #6	$241.57	6.283%	$256.7478	$256.75	$256.75	$256.70
Purchase #7	$211.89	10.188%	$233.4774	$233.48	$233.50	$233.50
7 purchase totals =	$970.26		$1,042.9088	$1,042.91	$1,042.95	$1,042.90