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	$16.49	6.522%	$17.5655	$17.57	$17.55	$17.60
Purchase #2	$138.82	4.139%	$144.5658	$144.57	$144.55	$144.60
Purchase #3	$90.72	10.238%	$100.0079	$100.01	$100.00	$100.00
Purchase #4	$149.61	4.841%	$156.8526	$156.85	$156.85	$156.90
Purchase #5	$153.69	5.706%	$162.4596	$162.46	$162.45	$162.50
Purchase #6	$132.63	5.628%	$140.0944	$140.09	$140.10	$140.10
Purchase #7	$11.26	4.213%	$11.7344	$11.73	$11.75	$11.70
7 purchase totals =	$693.22		$733.2802	$733.28	$733.25	$733.40