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	$70.68	13.798%	$80.4324	$80.43	$80.45	$80.40
Purchase #2	$126.83	5.720%	$134.0847	$134.08	$134.10	$134.10
Purchase #3	$10.38	11.217%	$11.5443	$11.54	$11.55	$11.50
Purchase #4	$247.39	11.552%	$275.9685	$275.97	$275.95	$276.00
Purchase #5	$138.71	4.208%	$144.5469	$144.55	$144.55	$144.50
Purchase #6	$244.51	11.681%	$273.0712	$273.07	$273.05	$273.10
Purchase #7	$90.76	13.573%	$103.0789	$103.08	$103.10	$103.10
7 purchase totals =	$929.26		$1,022.7269	$1,022.72	$1,022.75	$1,022.70