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	$100.99	10.509%	$111.603	$111.60	$111.60	$111.60
Purchase #2	$185.93	13.746%	$211.4879	$211.49	$211.50	$211.50
Purchase #3	$18.80	12.398%	$21.1308	$21.13	$21.15	$21.10
Purchase #4	$105.27	11.368%	$117.2371	$117.24	$117.25	$117.20
Purchase #5	$31.59	6.206%	$33.5505	$33.55	$33.55	$33.60
Purchase #6	$40.84	5.344%	$43.0225	$43.02	$43.00	$43.00
Purchase #7	$141.34	12.304%	$158.7305	$158.73	$158.75	$158.70
7 purchase totals =	$624.76		$696.7623	$696.76	$696.80	$696.70