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	$244.87	3.590%	$253.6608	$253.66	$253.65	$253.70
Purchase #2	$43.30	7.298%	$46.46	$46.46	$46.45	$46.50
Purchase #3	$101.89	3.137%	$105.0863	$105.09	$105.10	$105.10
Purchase #4	$120.90	13.848%	$137.6422	$137.64	$137.65	$137.60
Purchase #5	$18.68	11.719%	$20.8691	$20.87	$20.85	$20.90
Purchase #6	$84.62	6.426%	$90.0577	$90.06	$90.05	$90.10
Purchase #7	$146.82	11.730%	$164.042	$164.04	$164.05	$164.00
7 purchase totals =	$761.08		$817.8181	$817.82	$817.80	$817.90