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	$51.38	6.256%	$54.5943	$54.59	$54.60	$54.60
Purchase #2	$138.90	5.382%	$146.3756	$146.38	$146.40	$146.40
Purchase #3	$139.79	8.184%	$151.2304	$151.23	$151.25	$151.20
Purchase #4	$77.80	9.596%	$85.2657	$85.27	$85.25	$85.30
Purchase #5	$76.35	5.501%	$80.55	$80.55	$80.55	$80.60
Purchase #6	$10.31	10.560%	$11.3987	$11.40	$11.40	$11.40
Purchase #7	$100.75	5.227%	$106.0162	$106.02	$106.00	$106.00
7 purchase totals =	$595.28		$635.4309	$635.44	$635.45	$635.50