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	$102.50	12.620%	$115.4355	$115.44	$115.45	$115.40
Purchase #2	$95.25	9.864%	$104.6455	$104.65	$104.65	$104.60
Purchase #3	$163.67	5.851%	$173.2463	$173.25	$173.25	$173.20
Purchase #4	$100.42	4.456%	$104.8947	$104.89	$104.90	$104.90
Purchase #5	$133.29	3.244%	$137.6139	$137.61	$137.60	$137.60
Purchase #6	$105.78	12.375%	$118.8703	$118.87	$118.85	$118.90
Purchase #7	$166.78	5.823%	$176.4916	$176.49	$176.50	$176.50
7 purchase totals =	$867.69		$931.1978	$931.20	$931.20	$931.10