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	$44.58	10.162%	$49.1102	$49.11	$49.10	$49.10
Purchase #2	$42.72	6.806%	$45.6275	$45.63	$45.65	$45.60
Purchase #3	$203.33	9.807%	$223.2706	$223.27	$223.25	$223.30
Purchase #4	$138.64	13.708%	$157.6448	$157.64	$157.65	$157.60
Purchase #5	$154.59	7.239%	$165.7808	$165.78	$165.80	$165.80
Purchase #6	$62.59	4.635%	$65.491	$65.49	$65.50	$65.50
Purchase #7	$139.50	11.750%	$155.8913	$155.89	$155.90	$155.90
7 purchase totals =	$785.95		$862.8162	$862.81	$862.85	$862.80