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	$134.57	7.423%	$144.5591	$144.56	$144.55	$144.60
Purchase #2	$164.45	9.495%	$180.0645	$180.06	$180.05	$180.10
Purchase #3	$39.78	11.839%	$44.4896	$44.49	$44.50	$44.50
Purchase #4	$100.91	4.491%	$105.4419	$105.44	$105.45	$105.40
Purchase #5	$51.86	10.679%	$57.3981	$57.40	$57.40	$57.40
Purchase #6	$176.34	8.116%	$190.6518	$190.65	$190.65	$190.70
Purchase #7	$6.57	12.117%	$7.3661	$7.37	$7.35	$7.40
7 purchase totals =	$674.48		$729.9711	$729.97	$729.95	$730.10