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	$49.98	13.198%	$56.5764	$56.58	$56.60	$56.60
Purchase #2	$186.67	5.239%	$196.4496	$196.45	$196.45	$196.40
Purchase #3	$9.46	3.325%	$9.7745	$9.77	$9.75	$9.80
Purchase #4	$56.63	5.111%	$59.5244	$59.52	$59.50	$59.50
Purchase #5	$35.71	8.263%	$38.6607	$38.66	$38.65	$38.70
Purchase #6	$136.51	3.244%	$140.9384	$140.94	$140.95	$140.90
Purchase #7	$104.47	12.476%	$117.5037	$117.50	$117.50	$117.50
7 purchase totals =	$579.43		$619.4277	$619.42	$619.40	$619.40