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	$160.25	12.155%	$179.7284	$179.73	$179.75	$179.70
Purchase #2	$21.31	9.748%	$23.3873	$23.39	$23.40	$23.40
Purchase #3	$159.46	10.403%	$176.0486	$176.05	$176.05	$176.00
Purchase #4	$46.87	13.566%	$53.2284	$53.23	$53.25	$53.20
Purchase #5	$138.46	11.868%	$154.8924	$154.89	$154.90	$154.90
Purchase #6	$13.56	11.105%	$15.0658	$15.07	$15.05	$15.10
Purchase #7	$61.63	8.534%	$66.8895	$66.89	$66.90	$66.90
7 purchase totals =	$601.54		$669.2404	$669.25	$669.30	$669.20