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	$132.62	6.688%	$141.4896	$141.49	$141.50	$141.50
Purchase #2	$190.25	9.597%	$208.5083	$208.51	$208.50	$208.50
Purchase #3	$220.78	11.348%	$245.8341	$245.83	$245.85	$245.80
Purchase #4	$27.60	3.391%	$28.5359	$28.54	$28.55	$28.50
Purchase #5	$195.64	7.153%	$209.6341	$209.63	$209.65	$209.60
Purchase #6	$23.39	8.105%	$25.2858	$25.29	$25.30	$25.30
Purchase #7	$55.32	10.679%	$61.2276	$61.23	$61.25	$61.20
7 purchase totals =	$845.60		$920.5154	$920.52	$920.60	$920.40