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	$29.57	9.537%	$32.3901	$32.39	$32.40	$32.40
Purchase #2	$118.77	4.275%	$123.8474	$123.85	$123.85	$123.80
Purchase #3	$132.51	10.743%	$146.7455	$146.75	$146.75	$146.70
Purchase #4	$231.48	9.425%	$253.297	$253.30	$253.30	$253.30
Purchase #5	$122.89	11.694%	$137.2608	$137.26	$137.25	$137.30
Purchase #6	$132.87	10.348%	$146.6194	$146.62	$146.60	$146.60
Purchase #7	$222.92	9.776%	$244.7127	$244.71	$244.70	$244.70
7 purchase totals =	$991.01		$1,084.8729	$1,084.88	$1,084.85	$1,084.80