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	$70.83	13.598%	$80.4615	$80.46	$80.45	$80.50
Purchase #2	$228.96	3.764%	$237.5781	$237.58	$237.60	$237.60
Purchase #3	$88.49	13.784%	$100.6875	$100.69	$100.70	$100.70
Purchase #4	$48.37	13.599%	$54.9478	$54.95	$54.95	$54.90
Purchase #5	$11.89	5.115%	$12.4982	$12.50	$12.50	$12.50
Purchase #6	$170.41	4.504%	$178.0853	$178.09	$178.10	$178.10
Purchase #7	$61.76	9.780%	$67.8001	$67.80	$67.80	$67.80
7 purchase totals =	$680.71		$732.0585	$732.07	$732.10	$732.10