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	$99.93	6.537%	$106.4624	$106.46	$106.45	$106.50
Purchase #2	$56.64	5.621%	$59.8237	$59.82	$59.80	$59.80
Purchase #3	$138.70	13.793%	$157.8309	$157.83	$157.85	$157.80
Purchase #4	$162.25	12.265%	$182.15	$182.15	$182.15	$182.20
Purchase #5	$24.29	13.373%	$27.5383	$27.54	$27.55	$27.50
Purchase #6	$133.34	3.184%	$137.5855	$137.59	$137.60	$137.60
Purchase #7	$104.93	3.520%	$108.6235	$108.62	$108.60	$108.60
7 purchase totals =	$720.08		$780.0143	$780.01	$780.00	$780.00