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	$12.40	3.792%	$12.8702	$12.87	$12.85	$12.90
Purchase #2	$106.66	4.251%	$111.1941	$111.19	$111.20	$111.20
Purchase #3	$241.88	5.435%	$255.0262	$255.03	$255.05	$255.00
Purchase #4	$165.96	13.643%	$188.6019	$188.60	$188.60	$188.60
Purchase #5	$86.41	13.176%	$97.7954	$97.80	$97.80	$97.80
Purchase #6	$125.95	13.852%	$143.3966	$143.40	$143.40	$143.40
Purchase #7	$47.50	6.597%	$50.6336	$50.63	$50.65	$50.60
7 purchase totals =	$786.76		$859.5180	$859.52	$859.55	$859.50