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	$78.77	6.573%	$83.9476	$83.95	$83.95	$83.90
Purchase #2	$18.38	4.164%	$19.1453	$19.15	$19.15	$19.10
Purchase #3	$145.98	5.114%	$153.4454	$153.45	$153.45	$153.40
Purchase #4	$135.75	3.755%	$140.8474	$140.85	$140.85	$140.80
Purchase #5	$115.51	10.493%	$127.6305	$127.63	$127.65	$127.60
Purchase #6	$170.83	3.552%	$176.8979	$176.90	$176.90	$176.90
Purchase #7	$159.89	5.367%	$168.4713	$168.47	$168.45	$168.50
7 purchase totals =	$825.11		$870.3854	$870.40	$870.40	$870.20