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	$11.71	5.221%	$12.3214	$12.32	$12.30	$12.30
Purchase #2	$170.59	11.563%	$190.3153	$190.32	$190.30	$190.30
Purchase #3	$18.49	8.519%	$20.0652	$20.07	$20.05	$20.10
Purchase #4	$239.82	7.280%	$257.2789	$257.28	$257.30	$257.30
Purchase #5	$72.89	7.520%	$78.3713	$78.37	$78.35	$78.40
Purchase #6	$215.40	8.422%	$233.541	$233.54	$233.55	$233.50
Purchase #7	$44.58	9.475%	$48.804	$48.80	$48.80	$48.80
7 purchase totals =	$773.48		$840.6971	$840.70	$840.65	$840.70