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	$67.30	8.103%	$72.7533	$72.75	$72.75	$72.80
Purchase #2	$170.32	10.346%	$187.9413	$187.94	$187.95	$187.90
Purchase #3	$10.48	9.685%	$11.495	$11.50	$11.50	$11.50
Purchase #4	$116.97	5.105%	$122.9413	$122.94	$122.95	$122.90
Purchase #5	$97.34	3.202%	$100.4568	$100.46	$100.45	$100.50
Purchase #6	$85.61	5.172%	$90.0377	$90.04	$90.05	$90.00
Purchase #7	$11.66	13.274%	$13.2077	$13.21	$13.20	$13.20
7 purchase totals =	$559.68		$598.8331	$598.84	$598.85	$598.80