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	$222.52	13.704%	$253.0141	$253.01	$253.00	$253.00
Purchase #2	$172.78	8.187%	$186.9255	$186.93	$186.95	$186.90
Purchase #3	$241.46	12.599%	$271.8815	$271.88	$271.90	$271.90
Purchase #4	$232.45	5.870%	$246.0948	$246.09	$246.10	$246.10
Purchase #5	$115.33	4.772%	$120.8335	$120.83	$120.85	$120.80
Purchase #6	$132.85	3.400%	$137.3669	$137.37	$137.35	$137.40
Purchase #7	$100.26	11.493%	$111.7829	$111.78	$111.80	$111.80
7 purchase totals =	$1,217.65		$1,327.8992	$1,327.89	$1,327.95	$1,327.90