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	$223.56	12.239%	$250.9215	$250.92	$250.90	$250.90
Purchase #2	$155.67	6.422%	$165.6671	$165.67	$165.65	$165.70
Purchase #3	$125.39	11.194%	$139.4262	$139.43	$139.45	$139.40
Purchase #4	$100.26	4.613%	$104.885	$104.89	$104.90	$104.90
Purchase #5	$57.88	13.468%	$65.6753	$65.68	$65.70	$65.70
Purchase #6	$134.94	12.194%	$151.3946	$151.39	$151.40	$151.40
Purchase #7	$177.86	10.622%	$196.7523	$196.75	$196.75	$196.80
7 purchase totals =	$975.56		$1,074.7220	$1,074.73	$1,074.75	$1,074.80