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	$223.92	6.369%	$238.1815	$238.18	$238.20	$238.20
Purchase #2	$104.52	10.848%	$115.8583	$115.86	$115.85	$115.90
Purchase #3	$28.38	11.313%	$31.5906	$31.59	$31.60	$31.60
Purchase #4	$11.63	4.742%	$12.1815	$12.18	$12.20	$12.20
Purchase #5	$16.79	8.297%	$18.1831	$18.18	$18.20	$18.20
Purchase #6	$18.54	8.347%	$20.0875	$20.09	$20.10	$20.10
Purchase #7	$6.85	4.509%	$7.1589	$7.16	$7.15	$7.20
7 purchase totals =	$410.63		$443.2414	$443.24	$443.30	$443.40