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	$83.74	4.515%	$87.5209	$87.52	$87.50	$87.50
Purchase #2	$238.61	10.248%	$263.0628	$263.06	$263.05	$263.10
Purchase #3	$71.46	4.397%	$74.6021	$74.60	$74.60	$74.60
Purchase #4	$234.76	8.543%	$254.8155	$254.82	$254.80	$254.80
Purchase #5	$105.26	6.169%	$111.7535	$111.75	$111.75	$111.80
Purchase #6	$50.84	7.839%	$54.8253	$54.83	$54.85	$54.80
Purchase #7	$54.27	5.812%	$57.4242	$57.42	$57.40	$57.40
7 purchase totals =	$838.94		$904.0043	$904.00	$903.95	$904.00