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	$93.88	6.616%	$100.0911	$100.09	$100.10	$100.10
Purchase #2	$99.49	6.468%	$105.925	$105.93	$105.95	$105.90
Purchase #3	$49.32	8.376%	$53.451	$53.45	$53.45	$53.50
Purchase #4	$162.75	8.603%	$176.7514	$176.75	$176.75	$176.80
Purchase #5	$18.62	8.174%	$20.142	$20.14	$20.15	$20.10
Purchase #6	$21.75	4.359%	$22.6981	$22.70	$22.70	$22.70
Purchase #7	$107.29	4.735%	$112.3702	$112.37	$112.35	$112.40
7 purchase totals =	$553.10		$591.4288	$591.43	$591.45	$591.50