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	$27.31	13.563%	$31.0141	$31.01	$31.00	$31.00
Purchase #2	$127.78	3.378%	$132.0964	$132.10	$132.10	$132.10
Purchase #3	$177.89	7.181%	$190.6643	$190.66	$190.65	$190.70
Purchase #4	$45.98	6.184%	$48.8234	$48.82	$48.80	$48.80
Purchase #5	$96.77	12.298%	$108.6708	$108.67	$108.65	$108.70
Purchase #6	$41.35	10.227%	$45.5789	$45.58	$45.60	$45.60
Purchase #7	$19.58	3.165%	$20.1997	$20.20	$20.20	$20.20
7 purchase totals =	$536.66		$577.0476	$577.04	$577.00	$577.10