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	$240.55	6.723%	$256.7222	$256.72	$256.70	$256.70
Purchase #2	$42.91	6.159%	$45.5528	$45.55	$45.55	$45.60
Purchase #3	$147.59	5.523%	$155.7414	$155.74	$155.75	$155.70
Purchase #4	$236.60	4.224%	$246.594	$246.59	$246.60	$246.60
Purchase #5	$54.51	11.389%	$60.7181	$60.72	$60.70	$60.70
Purchase #6	$139.43	11.573%	$155.5662	$155.57	$155.55	$155.60
Purchase #7	$217.58	11.209%	$241.9685	$241.97	$241.95	$242.00
7 purchase totals =	$1,079.17		$1,162.8632	$1,162.86	$1,162.80	$1,162.90