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	$6.82	13.176%	$7.7186	$7.72	$7.70	$7.70
Purchase #2	$242.61	3.291%	$250.5943	$250.59	$250.60	$250.60
Purchase #3	$85.31	10.773%	$94.5004	$94.50	$94.50	$94.50
Purchase #4	$111.75	9.822%	$122.7261	$122.73	$122.75	$122.70
Purchase #5	$166.31	11.283%	$185.0748	$185.07	$185.05	$185.10
Purchase #6	$179.63	5.844%	$190.1276	$190.13	$190.15	$190.10
Purchase #7	$70.98	9.494%	$77.7188	$77.72	$77.70	$77.70
7 purchase totals =	$863.41		$928.4606	$928.46	$928.45	$928.40