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	$103.66	7.361%	$111.2904	$111.29	$111.30	$111.30
Purchase #2	$147.81	4.646%	$154.6773	$154.68	$154.70	$154.70
Purchase #3	$186.30	10.131%	$205.1741	$205.17	$205.15	$205.20
Purchase #4	$127.94	13.202%	$144.8306	$144.83	$144.85	$144.80
Purchase #5	$81.67	4.248%	$85.1393	$85.14	$85.15	$85.10
Purchase #6	$163.62	6.251%	$173.8479	$173.85	$173.85	$173.80
Purchase #7	$43.45	6.584%	$46.3107	$46.31	$46.30	$46.30
7 purchase totals =	$854.45		$921.2703	$921.27	$921.30	$921.20