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	$23.32	6.758%	$24.896	$24.90	$24.90	$24.90
Purchase #2	$95.77	9.325%	$104.7006	$104.70	$104.70	$104.70
Purchase #3	$16.50	8.458%	$17.8956	$17.90	$17.90	$17.90
Purchase #4	$92.63	12.679%	$104.3746	$104.37	$104.35	$104.40
Purchase #5	$55.70	12.174%	$62.4809	$62.48	$62.50	$62.50
Purchase #6	$44.45	10.550%	$49.1395	$49.14	$49.15	$49.10
Purchase #7	$35.86	5.866%	$37.9635	$37.96	$37.95	$38.00
7 purchase totals =	$364.23		$401.4507	$401.45	$401.45	$401.50