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	$10.26	6.114%	$10.8873	$10.89	$10.90	$10.90
Purchase #2	$62.27	5.445%	$65.6606	$65.66	$65.65	$65.70
Purchase #3	$93.78	9.612%	$102.7941	$102.79	$102.80	$102.80
Purchase #4	$231.89	10.734%	$256.7811	$256.78	$256.80	$256.80
Purchase #5	$134.42	10.520%	$148.561	$148.56	$148.55	$148.60
Purchase #6	$147.60	7.693%	$158.9549	$158.95	$158.95	$159.00
Purchase #7	$102.81	9.623%	$112.7034	$112.70	$112.70	$112.70
7 purchase totals =	$783.03		$856.3424	$856.33	$856.35	$856.50