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	$34.67	13.760%	$39.4406	$39.44	$39.45	$39.40
Purchase #2	$223.51	6.786%	$238.6774	$238.68	$238.70	$238.70
Purchase #3	$233.51	9.495%	$255.6818	$255.68	$255.70	$255.70
Purchase #4	$26.84	3.560%	$27.7955	$27.80	$27.80	$27.80
Purchase #5	$103.99	6.868%	$111.132	$111.13	$111.15	$111.10
Purchase #6	$43.92	11.105%	$48.7973	$48.80	$48.80	$48.80
Purchase #7	$167.92	10.467%	$185.4962	$185.50	$185.50	$185.50
7 purchase totals =	$834.36		$907.0208	$907.03	$907.10	$907.00