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	$75.58	6.665%	$80.6174	$80.62	$80.60	$80.60
Purchase #2	$80.63	8.241%	$87.2747	$87.27	$87.25	$87.30
Purchase #3	$42.71	8.228%	$46.2242	$46.22	$46.20	$46.20
Purchase #4	$173.84	6.863%	$185.7706	$185.77	$185.75	$185.80
Purchase #5	$63.45	12.241%	$71.2169	$71.22	$71.20	$71.20
Purchase #6	$143.77	6.154%	$152.6176	$152.62	$152.60	$152.60
Purchase #7	$85.70	4.382%	$89.4554	$89.46	$89.45	$89.50
7 purchase totals =	$665.68		$713.1768	$713.18	$713.05	$713.20