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	$34.29	9.355%	$37.4978	$37.50	$37.50	$37.50
Purchase #2	$35.46	4.629%	$37.1014	$37.10	$37.10	$37.10
Purchase #3	$9.51	5.822%	$10.0637	$10.06	$10.05	$10.10
Purchase #4	$55.42	8.826%	$60.3114	$60.31	$60.30	$60.30
Purchase #5	$115.31	11.537%	$128.6133	$128.61	$128.60	$128.60
Purchase #6	$230.93	11.588%	$257.6902	$257.69	$257.70	$257.70
Purchase #7	$71.54	6.450%	$76.1543	$76.15	$76.15	$76.20
7 purchase totals =	$552.46		$607.4321	$607.42	$607.40	$607.50