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	$55.90	3.265%	$57.7251	$57.73	$57.75	$57.70
Purchase #2	$185.89	8.581%	$201.8412	$201.84	$201.85	$201.80
Purchase #3	$27.87	13.802%	$31.7166	$31.72	$31.70	$31.70
Purchase #4	$106.54	4.758%	$111.6092	$111.61	$111.60	$111.60
Purchase #5	$217.78	10.150%	$239.8847	$239.88	$239.90	$239.90
Purchase #6	$191.72	4.422%	$200.1979	$200.20	$200.20	$200.20
Purchase #7	$19.90	8.424%	$21.5764	$21.58	$21.60	$21.60
7 purchase totals =	$805.60		$864.5511	$864.56	$864.60	$864.50