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	$128.36	8.169%	$138.8457	$138.85	$138.85	$138.80
Purchase #2	$188.61	4.240%	$196.6071	$196.61	$196.60	$196.60
Purchase #3	$234.28	10.819%	$259.6268	$259.63	$259.65	$259.60
Purchase #4	$208.70	8.316%	$226.0555	$226.06	$226.05	$226.10
Purchase #5	$97.51	3.480%	$100.9033	$100.90	$100.90	$100.90
Purchase #6	$105.86	12.734%	$119.3402	$119.34	$119.35	$119.30
Purchase #7	$237.52	9.235%	$259.455	$259.46	$259.45	$259.50
7 purchase totals =	$1,200.84		$1,300.8336	$1,300.85	$1,300.85	$1,300.80