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	$18.99	4.346%	$19.8153	$19.82	$19.80	$19.80
Purchase #2	$100.50	3.180%	$103.6959	$103.70	$103.70	$103.70
Purchase #3	$10.90	8.321%	$11.807	$11.81	$11.80	$11.80
Purchase #4	$246.71	7.609%	$265.4822	$265.48	$265.50	$265.50
Purchase #5	$159.70	13.759%	$181.6731	$181.67	$181.65	$181.70
Purchase #6	$190.85	8.214%	$206.5264	$206.53	$206.55	$206.50
Purchase #7	$205.90	10.499%	$227.5174	$227.52	$227.50	$227.50
7 purchase totals =	$933.55		$1,016.5173	$1,016.53	$1,016.50	$1,016.50