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	$222.68	10.209%	$245.4134	$245.41	$245.40	$245.40
Purchase #2	$10.94	13.265%	$12.3912	$12.39	$12.40	$12.40
Purchase #3	$102.62	8.488%	$111.3304	$111.33	$111.35	$111.30
Purchase #4	$172.41	13.856%	$196.2991	$196.30	$196.30	$196.30
Purchase #5	$58.70	11.164%	$65.2533	$65.25	$65.25	$65.30
Purchase #6	$44.48	8.216%	$48.1345	$48.13	$48.15	$48.10
Purchase #7	$151.52	5.504%	$159.8597	$159.86	$159.85	$159.90
7 purchase totals =	$763.35		$838.6816	$838.67	$838.70	$838.70