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	$107.82	3.768%	$111.8827	$111.88	$111.90	$111.90
Purchase #2	$76.50	13.408%	$86.7571	$86.76	$86.75	$86.80
Purchase #3	$134.83	5.211%	$141.856	$141.86	$141.85	$141.90
Purchase #4	$160.45	8.738%	$174.4701	$174.47	$174.45	$174.50
Purchase #5	$9.55	12.184%	$10.7136	$10.71	$10.70	$10.70
Purchase #6	$5.54	13.439%	$6.2845	$6.28	$6.30	$6.30
Purchase #7	$44.30	10.750%	$49.0623	$49.06	$49.05	$49.10
7 purchase totals =	$538.99		$581.0263	$581.02	$581.00	$581.20