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	$239.85	7.108%	$256.8985	$256.90	$256.90	$256.90
Purchase #2	$32.70	8.353%	$35.4314	$35.43	$35.45	$35.40
Purchase #3	$29.28	12.313%	$32.8852	$32.89	$32.90	$32.90
Purchase #4	$155.45	4.359%	$162.2261	$162.23	$162.25	$162.20
Purchase #5	$175.60	3.118%	$181.0752	$181.08	$181.10	$181.10
Purchase #6	$19.66	10.325%	$21.6899	$21.69	$21.70	$21.70
Purchase #7	$245.35	12.592%	$276.2445	$276.24	$276.25	$276.20
7 purchase totals =	$897.89		$966.4508	$966.46	$966.55	$966.40