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	$60.41	10.436%	$66.7144	$66.71	$66.70	$66.70
Purchase #2	$111.41	10.642%	$123.2663	$123.27	$123.25	$123.30
Purchase #3	$64.66	3.305%	$66.797	$66.80	$66.80	$66.80
Purchase #4	$86.81	5.531%	$91.6115	$91.61	$91.60	$91.60
Purchase #5	$191.57	8.741%	$208.3151	$208.32	$208.30	$208.30
Purchase #6	$102.82	5.642%	$108.6211	$108.62	$108.60	$108.60
Purchase #7	$19.75	7.481%	$21.2275	$21.23	$21.25	$21.20
7 purchase totals =	$637.43		$686.5529	$686.56	$686.50	$686.50