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	$103.81	7.392%	$111.4836	$111.48	$111.50	$111.50
Purchase #2	$84.83	11.837%	$94.8713	$94.87	$94.85	$94.90
Purchase #3	$50.32	12.643%	$56.682	$56.68	$56.70	$56.70
Purchase #4	$160.64	10.122%	$176.9	$176.90	$176.90	$176.90
Purchase #5	$80.79	11.332%	$89.9451	$89.95	$89.95	$89.90
Purchase #6	$153.75	9.508%	$168.3686	$168.37	$168.35	$168.40
Purchase #7	$146.74	4.339%	$153.107	$153.11	$153.10	$153.10
7 purchase totals =	$780.88		$851.3576	$851.36	$851.35	$851.40