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	$63.81	4.418%	$66.6291	$66.63	$66.65	$66.60
Purchase #2	$54.62	11.776%	$61.0521	$61.05	$61.05	$61.10
Purchase #3	$131.96	4.304%	$137.6396	$137.64	$137.65	$137.60
Purchase #4	$198.97	11.859%	$222.5659	$222.57	$222.55	$222.60
Purchase #5	$135.58	8.310%	$146.8467	$146.85	$146.85	$146.80
Purchase #6	$195.94	10.145%	$215.8181	$215.82	$215.80	$215.80
Purchase #7	$77.55	4.521%	$81.056	$81.06	$81.05	$81.10
7 purchase totals =	$858.43		$931.6075	$931.62	$931.60	$931.60