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	$60.33	9.720%	$66.1941	$66.19	$66.20	$66.20
Purchase #2	$68.67	5.251%	$72.2759	$72.28	$72.30	$72.30
Purchase #3	$50.62	10.256%	$55.8116	$55.81	$55.80	$55.80
Purchase #4	$199.58	11.803%	$223.1364	$223.14	$223.15	$223.10
Purchase #5	$51.39	4.870%	$53.8927	$53.89	$53.90	$53.90
Purchase #6	$87.60	13.826%	$99.7116	$99.71	$99.70	$99.70
Purchase #7	$14.41	4.170%	$15.0109	$15.01	$15.00	$15.00
7 purchase totals =	$532.60		$586.0332	$586.03	$586.05	$586.00