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	$50.51	8.579%	$54.8433	$54.84	$54.85	$54.80
Purchase #2	$47.57	6.763%	$50.7872	$50.79	$50.80	$50.80
Purchase #3	$103.61	3.802%	$107.5493	$107.55	$107.55	$107.50
Purchase #4	$119.96	10.413%	$132.4514	$132.45	$132.45	$132.50
Purchase #5	$142.86	8.552%	$155.0774	$155.08	$155.10	$155.10
Purchase #6	$10.35	6.331%	$11.0053	$11.01	$11.00	$11.00
Purchase #7	$149.74	4.273%	$156.1384	$156.14	$156.15	$156.10
7 purchase totals =	$624.60		$667.8523	$667.86	$667.90	$667.80