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	$70.25	8.658%	$76.3322	$76.33	$76.35	$76.30
Purchase #2	$69.92	7.453%	$75.1311	$75.13	$75.15	$75.10
Purchase #3	$168.60	5.629%	$178.0905	$178.09	$178.10	$178.10
Purchase #4	$81.45	10.804%	$90.2499	$90.25	$90.25	$90.20
Purchase #5	$71.39	9.364%	$78.075	$78.08	$78.10	$78.10
Purchase #6	$19.80	9.694%	$21.7194	$21.72	$21.70	$21.70
Purchase #7	$109.82	13.399%	$124.5348	$124.53	$124.55	$124.50
7 purchase totals =	$591.23		$644.1329	$644.13	$644.20	$644.00