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	$178.81	12.303%	$200.809	$200.81	$200.80	$200.80
Purchase #2	$160.91	8.677%	$174.8722	$174.87	$174.85	$174.90
Purchase #3	$69.29	3.244%	$71.5378	$71.54	$71.55	$71.50
Purchase #4	$106.91	6.186%	$113.5235	$113.52	$113.50	$113.50
Purchase #5	$38.50	4.542%	$40.2487	$40.25	$40.25	$40.20
Purchase #6	$171.25	7.277%	$183.7119	$183.71	$183.70	$183.70
Purchase #7	$158.50	11.321%	$176.4438	$176.44	$176.45	$176.40
7 purchase totals =	$884.17		$961.1469	$961.14	$961.10	$961.00