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	$18.39	6.508%	$19.5868	$19.59	$19.60	$19.60
Purchase #2	$112.76	9.429%	$123.3921	$123.39	$123.40	$123.40
Purchase #3	$176.49	8.647%	$191.7511	$191.75	$191.75	$191.80
Purchase #4	$10.74	8.213%	$11.6221	$11.62	$11.60	$11.60
Purchase #5	$45.60	12.817%	$51.4446	$51.44	$51.45	$51.40
Purchase #6	$47.25	10.251%	$52.0936	$52.09	$52.10	$52.10
Purchase #7	$71.69	12.485%	$80.6405	$80.64	$80.65	$80.60
7 purchase totals =	$482.92		$530.5308	$530.52	$530.55	$530.50