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	$14.92	8.491%	$16.1869	$16.19	$16.20	$16.20
Purchase #2	$230.98	6.615%	$246.2593	$246.26	$246.25	$246.30
Purchase #3	$149.85	13.715%	$170.4019	$170.40	$170.40	$170.40
Purchase #4	$72.93	13.260%	$82.6005	$82.60	$82.60	$82.60
Purchase #5	$82.28	11.230%	$91.52	$91.52	$91.50	$91.50
Purchase #6	$19.57	4.341%	$20.4195	$20.42	$20.40	$20.40
Purchase #7	$39.89	6.283%	$42.3963	$42.40	$42.40	$42.40
7 purchase totals =	$610.42		$669.7844	$669.79	$669.75	$669.80