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	$63.28	8.159%	$68.443	$68.44	$68.45	$68.40
Purchase #2	$139.66	13.166%	$158.0476	$158.05	$158.05	$158.00
Purchase #3	$82.33	10.247%	$90.7664	$90.77	$90.75	$90.80
Purchase #4	$6.90	8.223%	$7.4674	$7.47	$7.45	$7.50
Purchase #5	$132.84	7.521%	$142.8309	$142.83	$142.85	$142.80
Purchase #6	$25.45	12.592%	$28.6547	$28.65	$28.65	$28.70
Purchase #7	$9.47	11.729%	$10.5807	$10.58	$10.60	$10.60
7 purchase totals =	$459.93		$506.7907	$506.79	$506.80	$506.80