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	$76.45	9.509%	$83.7196	$83.72	$83.70	$83.70
Purchase #2	$17.69	13.627%	$20.1006	$20.10	$20.10	$20.10
Purchase #3	$170.27	12.834%	$192.1225	$192.12	$192.10	$192.10
Purchase #4	$55.66	8.189%	$60.218	$60.22	$60.20	$60.20
Purchase #5	$19.41	5.523%	$20.482	$20.48	$20.50	$20.50
Purchase #6	$51.78	8.152%	$56.0011	$56.00	$56.00	$56.00
Purchase #7	$82.27	5.149%	$86.5061	$86.51	$86.50	$86.50
7 purchase totals =	$473.53		$519.1499	$519.15	$519.10	$519.10