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	$30.99	8.379%	$33.5867	$33.59	$33.60	$33.60
Purchase #2	$168.90	7.848%	$182.1553	$182.16	$182.15	$182.20
Purchase #3	$52.50	13.607%	$59.6437	$59.64	$59.65	$59.60
Purchase #4	$47.72	3.748%	$49.5085	$49.51	$49.50	$49.50
Purchase #5	$157.88	4.780%	$165.4267	$165.43	$165.45	$165.40
Purchase #6	$95.87	10.456%	$105.8942	$105.89	$105.90	$105.90
Purchase #7	$184.78	11.312%	$205.6823	$205.68	$205.70	$205.70
7 purchase totals =	$738.64		$801.8974	$801.90	$801.95	$801.90