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	$71.28	12.824%	$80.4209	$80.42	$80.40	$80.40
Purchase #2	$238.32	6.395%	$253.5606	$253.56	$253.55	$253.60
Purchase #3	$72.66	11.566%	$81.0639	$81.06	$81.05	$81.10
Purchase #4	$215.35	10.386%	$237.7163	$237.72	$237.70	$237.70
Purchase #5	$61.76	9.385%	$67.5562	$67.56	$67.55	$67.60
Purchase #6	$89.67	6.554%	$95.547	$95.55	$95.55	$95.50
Purchase #7	$45.45	7.533%	$48.8737	$48.87	$48.85	$48.90
7 purchase totals =	$794.49		$864.7386	$864.74	$864.65	$864.80