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	$72.57	9.538%	$79.4917	$79.49	$79.50	$79.50
Purchase #2	$199.94	13.182%	$226.2961	$226.30	$226.30	$226.30
Purchase #3	$175.25	10.511%	$193.6705	$193.67	$193.65	$193.70
Purchase #4	$247.55	13.149%	$280.1003	$280.10	$280.10	$280.10
Purchase #5	$60.65	3.131%	$62.549	$62.55	$62.55	$62.50
Purchase #6	$109.36	13.237%	$123.836	$123.84	$123.85	$123.80
Purchase #7	$112.39	6.344%	$119.52	$119.52	$119.50	$119.50
7 purchase totals =	$977.71		$1,085.4636	$1,085.47	$1,085.45	$1,085.40