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	$160.45	7.366%	$172.2687	$172.27	$172.25	$172.30
Purchase #2	$222.51	8.434%	$241.2765	$241.28	$241.30	$241.30
Purchase #3	$20.62	7.314%	$22.1281	$22.13	$22.15	$22.10
Purchase #4	$207.79	7.508%	$223.3909	$223.39	$223.40	$223.40
Purchase #5	$84.37	5.408%	$88.9327	$88.93	$88.95	$88.90
Purchase #6	$148.67	13.580%	$168.8594	$168.86	$168.85	$168.90
Purchase #7	$11.26	5.856%	$11.9194	$11.92	$11.90	$11.90
7 purchase totals =	$855.67		$928.7757	$928.78	$928.80	$928.80