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	$56.65	7.759%	$61.0455	$61.05	$61.05	$61.00
Purchase #2	$48.29	13.492%	$54.8053	$54.81	$54.80	$54.80
Purchase #3	$183.97	13.310%	$208.4564	$208.46	$208.45	$208.50
Purchase #4	$155.82	6.467%	$165.8969	$165.90	$165.90	$165.90
Purchase #5	$231.93	8.237%	$251.0341	$251.03	$251.05	$251.00
Purchase #6	$111.33	10.579%	$123.1076	$123.11	$123.10	$123.10
Purchase #7	$127.67	9.277%	$139.5139	$139.51	$139.50	$139.50
7 purchase totals =	$915.66		$1,003.8597	$1,003.87	$1,003.85	$1,003.80