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	$235.82	10.361%	$260.2533	$260.25	$260.25	$260.30
Purchase #2	$169.85	8.806%	$184.807	$184.81	$184.80	$184.80
Purchase #3	$30.33	12.710%	$34.1849	$34.18	$34.20	$34.20
Purchase #4	$103.76	6.475%	$110.4785	$110.48	$110.50	$110.50
Purchase #5	$111.61	10.244%	$123.0433	$123.04	$123.05	$123.00
Purchase #6	$212.93	7.750%	$229.4321	$229.43	$229.45	$229.40
Purchase #7	$193.54	7.776%	$208.5897	$208.59	$208.60	$208.60
7 purchase totals =	$1,057.84		$1,150.7888	$1,150.78	$1,150.85	$1,150.80