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	$44.78	13.643%	$50.8893	$50.89	$50.90	$50.90
Purchase #2	$245.42	13.622%	$278.8511	$278.85	$278.85	$278.90
Purchase #3	$42.29	10.540%	$46.7474	$46.75	$46.75	$46.70
Purchase #4	$82.25	9.651%	$90.1879	$90.19	$90.20	$90.20
Purchase #5	$135.72	8.141%	$146.769	$146.77	$146.75	$146.80
Purchase #6	$101.81	13.208%	$115.2571	$115.26	$115.25	$115.30
Purchase #7	$203.25	10.134%	$223.8474	$223.85	$223.85	$223.80
7 purchase totals =	$855.52		$952.5492	$952.56	$952.55	$952.60