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	$50.52	13.712%	$57.4473	$57.45	$57.45	$57.40
Purchase #2	$144.60	4.729%	$151.4381	$151.44	$151.45	$151.40
Purchase #3	$228.82	6.668%	$244.0777	$244.08	$244.10	$244.10
Purchase #4	$146.66	4.194%	$152.8109	$152.81	$152.80	$152.80
Purchase #5	$153.83	3.172%	$158.7095	$158.71	$158.70	$158.70
Purchase #6	$175.66	6.476%	$187.0357	$187.04	$187.05	$187.00
Purchase #7	$34.34	13.365%	$38.9295	$38.93	$38.95	$38.90
7 purchase totals =	$934.43		$990.4487	$990.46	$990.50	$990.30