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	$48.55	4.669%	$50.8168	$50.82	$50.80	$50.80
Purchase #2	$198.53	13.548%	$225.4268	$225.43	$225.45	$225.40
Purchase #3	$109.75	8.156%	$118.7012	$118.70	$118.70	$118.70
Purchase #4	$114.83	10.654%	$127.064	$127.06	$127.05	$127.10
Purchase #5	$127.69	7.758%	$137.5962	$137.60	$137.60	$137.60
Purchase #6	$147.29	12.308%	$165.4185	$165.42	$165.40	$165.40
Purchase #7	$43.29	11.339%	$48.1987	$48.20	$48.20	$48.20
7 purchase totals =	$789.93		$873.2222	$873.23	$873.20	$873.20