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	$120.73	7.403%	$129.6676	$129.67	$129.65	$129.70
Purchase #2	$30.60	8.279%	$33.1334	$33.13	$33.15	$33.10
Purchase #3	$177.85	6.168%	$188.8198	$188.82	$188.80	$188.80
Purchase #4	$103.80	4.188%	$108.1471	$108.15	$108.15	$108.10
Purchase #5	$25.41	10.710%	$28.1314	$28.13	$28.15	$28.10
Purchase #6	$158.68	8.388%	$171.9901	$171.99	$172.00	$172.00
Purchase #7	$7.40	6.117%	$7.8527	$7.85	$7.85	$7.90
7 purchase totals =	$624.47		$667.7421	$667.74	$667.75	$667.70