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	$160.75	5.798%	$170.0703	$170.07	$170.05	$170.10
Purchase #2	$88.85	12.797%	$100.2201	$100.22	$100.20	$100.20
Purchase #3	$20.65	13.194%	$23.3746	$23.37	$23.35	$23.40
Purchase #4	$5.72	4.626%	$5.9846	$5.98	$6.00	$6.00
Purchase #5	$44.80	13.333%	$50.7732	$50.77	$50.75	$50.80
Purchase #6	$100.82	10.109%	$111.0119	$111.01	$111.00	$111.00
Purchase #7	$168.89	13.123%	$191.0534	$191.05	$191.05	$191.10
7 purchase totals =	$590.48		$652.4881	$652.47	$652.40	$652.60