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	$108.41	3.250%	$111.9333	$111.93	$111.95	$111.90
Purchase #2	$134.28	11.392%	$149.5772	$149.58	$149.60	$149.60
Purchase #3	$199.52	11.720%	$222.9037	$222.90	$222.90	$222.90
Purchase #4	$81.56	8.808%	$88.7438	$88.74	$88.75	$88.70
Purchase #5	$66.50	11.466%	$74.1249	$74.12	$74.10	$74.10
Purchase #6	$151.59	10.222%	$167.0855	$167.09	$167.10	$167.10
Purchase #7	$9.25	8.786%	$10.0627	$10.06	$10.05	$10.10
7 purchase totals =	$751.11		$824.4311	$824.42	$824.45	$824.40