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	$29.91	9.543%	$32.7643	$32.76	$32.75	$32.80
Purchase #2	$145.39	10.359%	$160.451	$160.45	$160.45	$160.50
Purchase #3	$155.88	13.533%	$176.9752	$176.98	$177.00	$177.00
Purchase #4	$216.66	11.256%	$241.0472	$241.05	$241.05	$241.00
Purchase #5	$60.70	5.229%	$63.874	$63.87	$63.85	$63.90
Purchase #6	$99.94	3.642%	$103.5798	$103.58	$103.60	$103.60
Purchase #7	$37.68	11.709%	$42.092	$42.09	$42.10	$42.10
7 purchase totals =	$746.16		$820.7835	$820.78	$820.80	$820.90