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	$27.74	12.530%	$31.2158	$31.22	$31.20	$31.20
Purchase #2	$96.77	7.769%	$104.2881	$104.29	$104.30	$104.30
Purchase #3	$180.81	5.512%	$190.7762	$190.78	$190.80	$190.80
Purchase #4	$58.85	10.363%	$64.9486	$64.95	$64.95	$64.90
Purchase #5	$51.94	8.348%	$56.276	$56.28	$56.30	$56.30
Purchase #6	$17.65	7.442%	$18.9635	$18.96	$18.95	$19.00
Purchase #7	$154.60	11.778%	$172.8088	$172.81	$172.80	$172.80
7 purchase totals =	$588.36		$639.2770	$639.29	$639.30	$639.30