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	$45.97	12.867%	$51.885	$51.89	$51.90	$51.90
Purchase #2	$124.29	4.776%	$130.2261	$130.23	$130.25	$130.20
Purchase #3	$6.50	7.449%	$6.9842	$6.98	$7.00	$7.00
Purchase #4	$26.78	7.868%	$28.8871	$28.89	$28.90	$28.90
Purchase #5	$210.35	8.636%	$228.5158	$228.52	$228.50	$228.50
Purchase #6	$41.34	3.602%	$42.8291	$42.83	$42.85	$42.80
Purchase #7	$17.87	4.189%	$18.6186	$18.62	$18.60	$18.60
7 purchase totals =	$473.10		$507.9459	$507.96	$508.00	$507.90