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	$18.27	4.467%	$19.0861	$19.09	$19.10	$19.10
Purchase #2	$151.30	3.418%	$156.4714	$156.47	$156.45	$156.50
Purchase #3	$197.58	10.732%	$218.7843	$218.78	$218.80	$218.80
Purchase #4	$41.85	6.578%	$44.6029	$44.60	$44.60	$44.60
Purchase #5	$34.47	8.211%	$37.3003	$37.30	$37.30	$37.30
Purchase #6	$174.71	4.351%	$182.3116	$182.31	$182.30	$182.30
Purchase #7	$20.77	5.304%	$21.8716	$21.87	$21.85	$21.90
7 purchase totals =	$638.95		$680.4282	$680.42	$680.40	$680.50