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	$13.65	13.322%	$15.4685	$15.47	$15.45	$15.50
Purchase #2	$12.50	10.121%	$13.7651	$13.77	$13.75	$13.80
Purchase #3	$122.42	13.699%	$139.1903	$139.19	$139.20	$139.20
Purchase #4	$224.60	13.720%	$255.4151	$255.42	$255.40	$255.40
Purchase #5	$168.89	5.682%	$178.4863	$178.49	$178.50	$178.50
Purchase #6	$55.32	6.761%	$59.0602	$59.06	$59.05	$59.10
Purchase #7	$201.44	4.184%	$209.8682	$209.87	$209.85	$209.90
7 purchase totals =	$798.82		$871.2537	$871.27	$871.20	$871.40