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	$235.89	8.284%	$255.4311	$255.43	$255.45	$255.40
Purchase #2	$223.32	9.495%	$244.5242	$244.52	$244.50	$244.50
Purchase #3	$61.60	6.765%	$65.7672	$65.77	$65.75	$65.80
Purchase #4	$48.41	7.562%	$52.0708	$52.07	$52.05	$52.10
Purchase #5	$144.85	8.113%	$156.6017	$156.60	$156.60	$156.60
Purchase #6	$217.47	8.801%	$236.6095	$236.61	$236.60	$236.60
Purchase #7	$106.26	5.110%	$111.6899	$111.69	$111.70	$111.70
7 purchase totals =	$1,037.80		$1,122.6944	$1,122.69	$1,122.65	$1,122.70