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	$137.39	4.313%	$143.3156	$143.32	$143.30	$143.30
Purchase #2	$29.93	3.348%	$30.9321	$30.93	$30.95	$30.90
Purchase #3	$89.63	7.142%	$96.0314	$96.03	$96.05	$96.00
Purchase #4	$82.46	9.776%	$90.5213	$90.52	$90.50	$90.50
Purchase #5	$39.51	4.287%	$41.2038	$41.20	$41.20	$41.20
Purchase #6	$154.36	12.369%	$173.4528	$173.45	$173.45	$173.50
Purchase #7	$208.30	8.189%	$225.3577	$225.36	$225.35	$225.40
7 purchase totals =	$741.58		$800.8147	$800.81	$800.80	$800.80