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	$44.78	11.226%	$49.807	$49.81	$49.80	$49.80
Purchase #2	$80.72	7.338%	$86.6432	$86.64	$86.65	$86.60
Purchase #3	$133.78	7.172%	$143.3747	$143.37	$143.35	$143.40
Purchase #4	$19.71	7.105%	$21.1104	$21.11	$21.10	$21.10
Purchase #5	$64.82	11.228%	$72.098	$72.10	$72.10	$72.10
Purchase #6	$127.85	12.488%	$143.8159	$143.82	$143.80	$143.80
Purchase #7	$61.41	8.654%	$66.7244	$66.72	$66.70	$66.70
7 purchase totals =	$533.07		$583.5736	$583.57	$583.50	$583.50