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	$54.47	3.343%	$56.2909	$56.29	$56.30	$56.30
Purchase #2	$138.64	12.497%	$155.9658	$155.97	$155.95	$156.00
Purchase #3	$162.73	4.490%	$170.0366	$170.04	$170.05	$170.00
Purchase #4	$96.51	6.224%	$102.5168	$102.52	$102.50	$102.50
Purchase #5	$106.60	4.281%	$111.1635	$111.16	$111.15	$111.20
Purchase #6	$184.59	8.537%	$200.3484	$200.35	$200.35	$200.30
Purchase #7	$80.75	5.818%	$85.448	$85.45	$85.45	$85.40
7 purchase totals =	$824.29		$881.7700	$881.78	$881.75	$881.70