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	$7.48	8.798%	$8.1381	$8.14	$8.15	$8.10
Purchase #2	$118.78	3.117%	$122.4824	$122.48	$122.50	$122.50
Purchase #3	$235.74	11.358%	$262.5153	$262.52	$262.50	$262.50
Purchase #4	$93.76	7.584%	$100.8708	$100.87	$100.85	$100.90
Purchase #5	$5.96	13.758%	$6.78	$6.78	$6.80	$6.80
Purchase #6	$241.44	10.414%	$266.5836	$266.58	$266.60	$266.60
Purchase #7	$51.34	3.345%	$53.0573	$53.06	$53.05	$53.10
7 purchase totals =	$754.50		$820.4275	$820.43	$820.45	$820.50