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	$9.51	11.400%	$10.5941	$10.59	$10.60	$10.60
Purchase #2	$182.93	4.245%	$190.6954	$190.70	$190.70	$190.70
Purchase #3	$182.95	9.225%	$199.8271	$199.83	$199.85	$199.80
Purchase #4	$49.54	13.739%	$56.3463	$56.35	$56.35	$56.30
Purchase #5	$155.76	6.660%	$166.1336	$166.13	$166.15	$166.10
Purchase #6	$50.59	7.351%	$54.3089	$54.31	$54.30	$54.30
Purchase #7	$151.70	3.298%	$156.7031	$156.70	$156.70	$156.70
7 purchase totals =	$782.98		$834.6085	$834.61	$834.65	$834.50