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	$37.79	11.292%	$42.0572	$42.06	$42.05	$42.10
Purchase #2	$10.50	6.391%	$11.1711	$11.17	$11.15	$11.20
Purchase #3	$189.83	10.248%	$209.2838	$209.28	$209.30	$209.30
Purchase #4	$12.38	7.342%	$13.2889	$13.29	$13.30	$13.30
Purchase #5	$128.94	8.164%	$139.4667	$139.47	$139.45	$139.50
Purchase #6	$226.60	4.133%	$235.9654	$235.97	$235.95	$236.00
Purchase #7	$191.52	4.871%	$200.8489	$200.85	$200.85	$200.80
7 purchase totals =	$797.56		$852.0820	$852.09	$852.05	$852.20