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	$136.71	8.676%	$148.571	$148.57	$148.55	$148.60
Purchase #2	$150.72	5.776%	$159.4256	$159.43	$159.45	$159.40
Purchase #3	$42.62	6.603%	$45.4342	$45.43	$45.45	$45.40
Purchase #4	$65.45	5.808%	$69.2513	$69.25	$69.25	$69.30
Purchase #5	$214.75	7.845%	$231.5971	$231.60	$231.60	$231.60
Purchase #6	$38.71	13.381%	$43.8898	$43.89	$43.90	$43.90
Purchase #7	$69.71	8.310%	$75.5029	$75.50	$75.50	$75.50
7 purchase totals =	$718.67		$773.6719	$773.67	$773.70	$773.70