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	$165.79	3.655%	$171.8496	$171.85	$171.85	$171.80
Purchase #2	$137.48	6.846%	$146.8919	$146.89	$146.90	$146.90
Purchase #3	$217.39	8.313%	$235.4616	$235.46	$235.45	$235.50
Purchase #4	$204.37	9.131%	$223.031	$223.03	$223.05	$223.00
Purchase #5	$136.54	6.477%	$145.3837	$145.38	$145.40	$145.40
Purchase #6	$218.80	3.187%	$225.7732	$225.77	$225.75	$225.80
Purchase #7	$226.63	6.532%	$241.4335	$241.43	$241.45	$241.40
7 purchase totals =	$1,307.00		$1,389.8245	$1,389.81	$1,389.85	$1,389.80