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	$231.43	10.343%	$255.3668	$255.37	$255.35	$255.40
Purchase #2	$108.54	13.557%	$123.2548	$123.25	$123.25	$123.30
Purchase #3	$191.67	4.352%	$200.0115	$200.01	$200.00	$200.00
Purchase #4	$199.43	3.546%	$206.5018	$206.50	$206.50	$206.50
Purchase #5	$115.29	11.722%	$128.8043	$128.80	$128.80	$128.80
Purchase #6	$87.64	8.546%	$95.1297	$95.13	$95.15	$95.10
Purchase #7	$133.59	9.770%	$146.6417	$146.64	$146.65	$146.60
7 purchase totals =	$1,067.59		$1,155.7106	$1,155.70	$1,155.70	$1,155.70