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	$88.59	13.564%	$100.6063	$100.61	$100.60	$100.60
Purchase #2	$100.25	3.446%	$103.7046	$103.70	$103.70	$103.70
Purchase #3	$209.88	10.304%	$231.506	$231.51	$231.50	$231.50
Purchase #4	$62.61	12.869%	$70.6673	$70.67	$70.65	$70.70
Purchase #5	$124.95	9.871%	$137.2838	$137.28	$137.30	$137.30
Purchase #6	$53.32	8.714%	$57.9663	$57.97	$57.95	$58.00
Purchase #7	$13.52	9.581%	$14.8154	$14.82	$14.80	$14.80
7 purchase totals =	$653.12		$716.5497	$716.56	$716.50	$716.60