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	$121.39	5.471%	$128.0312	$128.03	$128.05	$128.00
Purchase #2	$159.86	3.624%	$165.6533	$165.65	$165.65	$165.70
Purchase #3	$101.93	9.803%	$111.9222	$111.92	$111.90	$111.90
Purchase #4	$77.71	7.572%	$83.5942	$83.59	$83.60	$83.60
Purchase #5	$109.79	6.618%	$117.0559	$117.06	$117.05	$117.10
Purchase #6	$63.50	3.328%	$65.6133	$65.61	$65.60	$65.60
Purchase #7	$176.38	4.730%	$184.7228	$184.72	$184.70	$184.70
7 purchase totals =	$810.56		$856.5929	$856.58	$856.55	$856.60