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	$11.49	6.847%	$12.2767	$12.28	$12.30	$12.30
Purchase #2	$148.69	4.151%	$154.8621	$154.86	$154.85	$154.90
Purchase #3	$114.62	8.259%	$124.0865	$124.09	$124.10	$124.10
Purchase #4	$47.83	4.393%	$49.9312	$49.93	$49.95	$49.90
Purchase #5	$90.25	11.753%	$100.8571	$100.86	$100.85	$100.90
Purchase #6	$190.47	5.284%	$200.5344	$200.53	$200.55	$200.50
Purchase #7	$28.61	10.215%	$31.5325	$31.53	$31.55	$31.50
7 purchase totals =	$631.96		$674.0805	$674.08	$674.15	$674.10