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	$111.78	12.800%	$126.0878	$126.09	$126.10	$126.10
Purchase #2	$70.92	10.476%	$78.3496	$78.35	$78.35	$78.30
Purchase #3	$105.35	4.675%	$110.2751	$110.28	$110.30	$110.30
Purchase #4	$212.53	5.264%	$223.7176	$223.72	$223.70	$223.70
Purchase #5	$127.80	3.312%	$132.0327	$132.03	$132.05	$132.00
Purchase #6	$130.33	10.240%	$143.6758	$143.68	$143.70	$143.70
Purchase #7	$111.82	6.235%	$118.792	$118.79	$118.80	$118.80
7 purchase totals =	$870.53		$932.9306	$932.94	$933.00	$932.90