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	$75.33	3.767%	$78.1677	$78.17	$78.15	$78.20
Purchase #2	$36.29	7.723%	$39.0927	$39.09	$39.10	$39.10
Purchase #3	$22.67	12.339%	$25.4673	$25.47	$25.45	$25.50
Purchase #4	$48.26	9.228%	$52.7134	$52.71	$52.70	$52.70
Purchase #5	$210.63	5.685%	$222.6043	$222.60	$222.60	$222.60
Purchase #6	$176.52	8.274%	$191.1253	$191.13	$191.15	$191.10
Purchase #7	$225.67	4.379%	$235.5521	$235.55	$235.55	$235.60
7 purchase totals =	$795.37		$844.7228	$844.72	$844.70	$844.80