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	$177.40	4.611%	$185.5799	$185.58	$185.60	$185.60
Purchase #2	$121.37	8.421%	$131.5906	$131.59	$131.60	$131.60
Purchase #3	$130.85	7.198%	$140.2686	$140.27	$140.25	$140.30
Purchase #4	$179.41	4.305%	$187.1336	$187.13	$187.15	$187.10
Purchase #5	$131.90	5.866%	$139.6373	$139.64	$139.65	$139.60
Purchase #6	$126.63	10.614%	$140.0705	$140.07	$140.05	$140.10
Purchase #7	$61.90	7.313%	$66.4267	$66.43	$66.45	$66.40
7 purchase totals =	$929.46		$990.7072	$990.71	$990.75	$990.70