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	$15.61	7.838%	$16.8335	$16.83	$16.85	$16.80
Purchase #2	$90.58	5.468%	$95.5329	$95.53	$95.55	$95.50
Purchase #3	$38.97	10.632%	$43.1133	$43.11	$43.10	$43.10
Purchase #4	$63.35	12.218%	$71.0901	$71.09	$71.10	$71.10
Purchase #5	$169.40	3.386%	$175.1359	$175.14	$175.15	$175.10
Purchase #6	$125.95	10.663%	$139.38	$139.38	$139.40	$139.40
Purchase #7	$136.64	5.408%	$144.0295	$144.03	$144.05	$144.00
7 purchase totals =	$640.50		$685.1152	$685.11	$685.20	$685.00