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	$166.68	3.737%	$172.9088	$172.91	$172.90	$172.90
Purchase #2	$82.32	9.613%	$90.2334	$90.23	$90.25	$90.20
Purchase #3	$175.51	11.342%	$195.4163	$195.42	$195.40	$195.40
Purchase #4	$17.65	11.748%	$19.7235	$19.72	$19.70	$19.70
Purchase #5	$241.26	7.642%	$259.6971	$259.70	$259.70	$259.70
Purchase #6	$11.66	10.105%	$12.8382	$12.84	$12.85	$12.80
Purchase #7	$196.43	13.416%	$222.783	$222.78	$222.80	$222.80
7 purchase totals =	$891.51		$973.6003	$973.60	$973.60	$973.50