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	$127.71	12.328%	$143.4541	$143.45	$143.45	$143.50
Purchase #2	$86.57	8.346%	$93.7951	$93.80	$93.80	$93.80
Purchase #3	$177.40	9.789%	$194.7657	$194.77	$194.75	$194.80
Purchase #4	$130.48	13.836%	$148.5332	$148.53	$148.55	$148.50
Purchase #5	$51.60	6.238%	$54.8188	$54.82	$54.80	$54.80
Purchase #6	$59.54	10.222%	$65.6262	$65.63	$65.65	$65.60
Purchase #7	$163.46	4.244%	$170.3972	$170.40	$170.40	$170.40
7 purchase totals =	$796.76		$871.3903	$871.40	$871.40	$871.40