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	$50.55	12.492%	$56.8647	$56.86	$56.85	$56.90
Purchase #2	$31.34	9.518%	$34.3229	$34.32	$34.30	$34.30
Purchase #3	$200.52	4.204%	$208.9499	$208.95	$208.95	$208.90
Purchase #4	$106.64	4.244%	$111.1658	$111.17	$111.15	$111.20
Purchase #5	$56.79	9.848%	$62.3827	$62.38	$62.40	$62.40
Purchase #6	$83.97	5.533%	$88.6161	$88.62	$88.60	$88.60
Purchase #7	$199.48	13.761%	$226.9304	$226.93	$226.95	$226.90
7 purchase totals =	$729.29		$789.2325	$789.23	$789.20	$789.20