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	$60.85	8.288%	$65.8932	$65.89	$65.90	$65.90
Purchase #2	$79.39	5.699%	$83.9144	$83.91	$83.90	$83.90
Purchase #3	$102.34	4.195%	$106.6332	$106.63	$106.65	$106.60
Purchase #4	$90.64	10.268%	$99.9469	$99.95	$99.95	$99.90
Purchase #5	$95.95	7.249%	$102.9054	$102.91	$102.90	$102.90
Purchase #6	$172.70	9.287%	$188.7386	$188.74	$188.75	$188.70
Purchase #7	$154.64	11.261%	$172.054	$172.05	$172.05	$172.10
7 purchase totals =	$756.51		$820.0857	$820.08	$820.10	$820.00