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	$21.59	10.340%	$23.8224	$23.82	$23.80	$23.80
Purchase #2	$105.70	7.513%	$113.6412	$113.64	$113.65	$113.60
Purchase #3	$98.89	12.735%	$111.4836	$111.48	$111.50	$111.50
Purchase #4	$70.36	13.123%	$79.5933	$79.59	$79.60	$79.60
Purchase #5	$56.60	5.536%	$59.7334	$59.73	$59.75	$59.70
Purchase #6	$100.51	13.170%	$113.7472	$113.75	$113.75	$113.70
Purchase #7	$165.49	11.611%	$184.705	$184.71	$184.70	$184.70
7 purchase totals =	$619.14		$686.7261	$686.72	$686.75	$686.60