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	$118.32	8.688%	$128.5996	$128.60	$128.60	$128.60
Purchase #2	$64.57	3.236%	$66.6595	$66.66	$66.65	$66.70
Purchase #3	$133.99	9.304%	$146.4564	$146.46	$146.45	$146.50
Purchase #4	$64.81	12.158%	$72.6896	$72.69	$72.70	$72.70
Purchase #5	$114.50	7.782%	$123.4104	$123.41	$123.40	$123.40
Purchase #6	$115.85	9.734%	$127.1268	$127.13	$127.15	$127.10
Purchase #7	$113.35	13.642%	$128.8132	$128.81	$128.80	$128.80
7 purchase totals =	$725.39		$793.7555	$793.76	$793.75	$793.80