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	$56.50	4.615%	$59.1075	$59.11	$59.10	$59.10
Purchase #2	$80.42	3.246%	$83.0304	$83.03	$83.05	$83.00
Purchase #3	$238.88	8.792%	$259.8823	$259.88	$259.90	$259.90
Purchase #4	$11.94	12.737%	$13.4608	$13.46	$13.45	$13.50
Purchase #5	$38.61	3.146%	$39.8247	$39.82	$39.80	$39.80
Purchase #6	$207.27	8.843%	$225.5989	$225.60	$225.60	$225.60
Purchase #7	$97.93	10.186%	$107.9051	$107.91	$107.90	$107.90
7 purchase totals =	$731.55		$788.8097	$788.81	$788.80	$788.80