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	$157.83	6.756%	$168.493	$168.49	$168.50	$168.50
Purchase #2	$184.81	8.230%	$200.0199	$200.02	$200.00	$200.00
Purchase #3	$162.82	9.549%	$178.3677	$178.37	$178.35	$178.40
Purchase #4	$48.61	5.660%	$51.3613	$51.36	$51.35	$51.40
Purchase #5	$124.88	12.569%	$140.5762	$140.58	$140.60	$140.60
Purchase #6	$143.75	4.479%	$150.1886	$150.19	$150.20	$150.20
Purchase #7	$11.57	8.174%	$12.5157	$12.52	$12.50	$12.50
7 purchase totals =	$834.27		$901.5224	$901.53	$901.50	$901.60