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	$97.70	10.613%	$108.0689	$108.07	$108.05	$108.10
Purchase #2	$43.29	6.105%	$45.9329	$45.93	$45.95	$45.90
Purchase #3	$92.56	11.771%	$103.4552	$103.46	$103.45	$103.50
Purchase #4	$174.95	8.615%	$190.0219	$190.02	$190.00	$190.00
Purchase #5	$218.25	5.135%	$229.4571	$229.46	$229.45	$229.50
Purchase #6	$150.79	5.544%	$159.1498	$159.15	$159.15	$159.10
Purchase #7	$123.52	7.325%	$132.5678	$132.57	$132.55	$132.60
7 purchase totals =	$901.06		$968.6536	$968.66	$968.60	$968.70