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	$80.55	3.769%	$83.5859	$83.59	$83.60	$83.60
Purchase #2	$84.88	7.707%	$91.4217	$91.42	$91.40	$91.40
Purchase #3	$117.97	12.653%	$132.8967	$132.90	$132.90	$132.90
Purchase #4	$65.41	3.574%	$67.7478	$67.75	$67.75	$67.70
Purchase #5	$100.37	10.677%	$111.0865	$111.09	$111.10	$111.10
Purchase #6	$21.74	3.521%	$22.5055	$22.51	$22.50	$22.50
Purchase #7	$100.97	4.634%	$105.6489	$105.65	$105.65	$105.60
7 purchase totals =	$571.89		$614.8930	$614.91	$614.90	$614.80