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	$181.54	12.536%	$204.2979	$204.30	$204.30	$204.30
Purchase #2	$83.40	6.369%	$88.7117	$88.71	$88.70	$88.70
Purchase #3	$226.33	8.733%	$246.0954	$246.10	$246.10	$246.10
Purchase #4	$82.57	13.206%	$93.4742	$93.47	$93.45	$93.50
Purchase #5	$105.98	5.395%	$111.6976	$111.70	$111.70	$111.70
Purchase #6	$35.70	4.805%	$37.4154	$37.42	$37.40	$37.40
Purchase #7	$14.41	5.706%	$15.2322	$15.23	$15.25	$15.20
7 purchase totals =	$729.93		$796.9244	$796.93	$796.90	$796.90