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	$220.35	10.198%	$242.8213	$242.82	$242.80	$242.80
Purchase #2	$210.94	6.726%	$225.1278	$225.13	$225.15	$225.10
Purchase #3	$23.72	5.772%	$25.0891	$25.09	$25.10	$25.10
Purchase #4	$95.80	13.243%	$108.4868	$108.49	$108.50	$108.50
Purchase #5	$37.63	13.736%	$42.7989	$42.80	$42.80	$42.80
Purchase #6	$18.93	12.571%	$21.3097	$21.31	$21.30	$21.30
Purchase #7	$18.60	5.411%	$19.6064	$19.61	$19.60	$19.60
7 purchase totals =	$625.97		$685.2400	$685.25	$685.25	$685.20