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	$10.40	6.429%	$11.0686	$11.07	$11.05	$11.10
Purchase #2	$138.31	13.509%	$156.9943	$156.99	$157.00	$157.00
Purchase #3	$141.28	12.455%	$158.8764	$158.88	$158.90	$158.90
Purchase #4	$146.72	10.532%	$162.1726	$162.17	$162.15	$162.20
Purchase #5	$144.64	4.714%	$151.4583	$151.46	$151.45	$151.50
Purchase #6	$45.76	10.414%	$50.5254	$50.53	$50.55	$50.50
Purchase #7	$31.77	6.318%	$33.7772	$33.78	$33.80	$33.80
7 purchase totals =	$658.88		$724.8728	$724.88	$724.90	$725.00