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	$71.59	12.380%	$80.4528	$80.45	$80.45	$80.50
Purchase #2	$239.89	5.594%	$253.3094	$253.31	$253.30	$253.30
Purchase #3	$90.43	13.746%	$102.8605	$102.86	$102.85	$102.90
Purchase #4	$108.48	4.252%	$113.0926	$113.09	$113.10	$113.10
Purchase #5	$119.50	3.657%	$123.8701	$123.87	$123.85	$123.90
Purchase #6	$123.30	12.722%	$138.9862	$138.99	$139.00	$139.00
Purchase #7	$148.59	12.741%	$167.5219	$167.52	$167.50	$167.50
7 purchase totals =	$901.78		$980.0935	$980.09	$980.05	$980.20