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	$93.46	6.563%	$99.5938	$99.59	$99.60	$99.60
Purchase #2	$56.86	4.672%	$59.5165	$59.52	$59.50	$59.50
Purchase #3	$71.48	5.626%	$75.5015	$75.50	$75.50	$75.50
Purchase #4	$149.95	3.627%	$155.3887	$155.39	$155.40	$155.40
Purchase #5	$15.58	13.204%	$17.6372	$17.64	$17.65	$17.60
Purchase #6	$30.68	5.463%	$32.356	$32.36	$32.35	$32.40
Purchase #7	$241.48	12.653%	$272.0345	$272.03	$272.05	$272.00
7 purchase totals =	$659.49		$712.0282	$712.03	$712.05	$712.00