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	$109.86	7.258%	$117.8336	$117.83	$117.85	$117.80
Purchase #2	$65.27	3.549%	$67.5864	$67.59	$67.60	$67.60
Purchase #3	$143.32	11.401%	$159.6599	$159.66	$159.65	$159.70
Purchase #4	$99.76	5.450%	$105.1969	$105.20	$105.20	$105.20
Purchase #5	$8.50	7.462%	$9.1343	$9.13	$9.15	$9.10
Purchase #6	$114.29	3.361%	$118.1313	$118.13	$118.15	$118.10
Purchase #7	$59.59	12.393%	$66.975	$66.98	$67.00	$67.00
7 purchase totals =	$600.59		$644.5174	$644.52	$644.60	$644.50