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	$246.47	13.559%	$279.8889	$279.89	$279.90	$279.90
Purchase #2	$159.46	8.308%	$172.7079	$172.71	$172.70	$172.70
Purchase #3	$76.82	11.114%	$85.3578	$85.36	$85.35	$85.40
Purchase #4	$118.88	6.203%	$126.2541	$126.25	$126.25	$126.30
Purchase #5	$74.83	5.494%	$78.9412	$78.94	$78.95	$78.90
Purchase #6	$85.94	13.349%	$97.4121	$97.41	$97.40	$97.40
Purchase #7	$54.77	7.485%	$58.8695	$58.87	$58.85	$58.90
7 purchase totals =	$817.17		$899.4315	$899.43	$899.40	$899.50