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	$138.67	10.848%	$153.7129	$153.71	$153.70	$153.70
Purchase #2	$135.60	5.763%	$143.4146	$143.41	$143.40	$143.40
Purchase #3	$61.32	9.103%	$66.902	$66.90	$66.90	$66.90
Purchase #4	$61.45	6.561%	$65.4817	$65.48	$65.50	$65.50
Purchase #5	$181.78	4.563%	$190.0746	$190.07	$190.05	$190.10
Purchase #6	$139.77	10.636%	$154.6359	$154.64	$154.65	$154.60
Purchase #7	$64.62	4.369%	$67.4432	$67.44	$67.45	$67.40
7 purchase totals =	$783.21		$841.6649	$841.65	$841.65	$841.60