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	$112.97	9.318%	$123.4965	$123.50	$123.50	$123.50
Purchase #2	$129.34	10.683%	$143.1574	$143.16	$143.15	$143.20
Purchase #3	$178.53	6.704%	$190.4987	$190.50	$190.50	$190.50
Purchase #4	$18.70	10.726%	$20.7058	$20.71	$20.70	$20.70
Purchase #5	$24.92	11.779%	$27.8553	$27.86	$27.85	$27.90
Purchase #6	$104.84	13.438%	$118.9284	$118.93	$118.95	$118.90
Purchase #7	$247.58	12.713%	$279.0548	$279.05	$279.05	$279.10
7 purchase totals =	$816.88		$903.6969	$903.71	$903.70	$903.80