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	$66.26	9.727%	$72.7051	$72.71	$72.70	$72.70
Purchase #2	$118.70	11.542%	$132.4004	$132.40	$132.40	$132.40
Purchase #3	$76.48	13.462%	$86.7757	$86.78	$86.80	$86.80
Purchase #4	$183.77	3.783%	$190.722	$190.72	$190.70	$190.70
Purchase #5	$6.68	5.631%	$7.0562	$7.06	$7.05	$7.10
Purchase #6	$77.79	6.611%	$82.9327	$82.93	$82.95	$82.90
Purchase #7	$241.87	10.208%	$266.5601	$266.56	$266.55	$266.60
7 purchase totals =	$771.55		$839.1522	$839.16	$839.15	$839.20