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	$59.55	3.249%	$61.4848	$61.48	$61.50	$61.50
Purchase #2	$60.85	9.657%	$66.7263	$66.73	$66.75	$66.70
Purchase #3	$30.55	7.824%	$32.9402	$32.94	$32.95	$32.90
Purchase #4	$129.73	10.719%	$143.6358	$143.64	$143.65	$143.60
Purchase #5	$222.54	8.239%	$240.8751	$240.88	$240.90	$240.90
Purchase #6	$29.64	13.753%	$33.7164	$33.72	$33.70	$33.70
Purchase #7	$25.60	5.467%	$26.9996	$27.00	$27.00	$27.00
7 purchase totals =	$558.46		$606.3782	$606.39	$606.45	$606.30