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	$13.43	13.551%	$15.2499	$15.25	$15.25	$15.20
Purchase #2	$137.25	13.420%	$155.669	$155.67	$155.65	$155.70
Purchase #3	$115.69	7.671%	$124.5646	$124.56	$124.55	$124.60
Purchase #4	$11.85	5.543%	$12.5068	$12.51	$12.50	$12.50
Purchase #5	$74.90	13.488%	$85.0025	$85.00	$85.00	$85.00
Purchase #6	$105.34	12.869%	$118.8962	$118.90	$118.90	$118.90
Purchase #7	$222.40	6.334%	$236.4868	$236.49	$236.50	$236.50
7 purchase totals =	$680.86		$748.3758	$748.38	$748.35	$748.40