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	$93.79	7.536%	$100.858	$100.86	$100.85	$100.90
Purchase #2	$114.63	12.115%	$128.5174	$128.52	$128.50	$128.50
Purchase #3	$24.59	8.103%	$26.5825	$26.58	$26.60	$26.60
Purchase #4	$150.64	3.289%	$155.5945	$155.59	$155.60	$155.60
Purchase #5	$239.64	5.786%	$253.5056	$253.51	$253.50	$253.50
Purchase #6	$101.83	12.336%	$114.3917	$114.39	$114.40	$114.40
Purchase #7	$31.39	7.606%	$33.7775	$33.78	$33.80	$33.80
7 purchase totals =	$756.51		$813.2272	$813.23	$813.25	$813.30