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	$50.98	13.583%	$57.9046	$57.90	$57.90	$57.90
Purchase #2	$176.46	13.167%	$199.6945	$199.69	$199.70	$199.70
Purchase #3	$151.34	7.852%	$163.2232	$163.22	$163.20	$163.20
Purchase #4	$133.94	8.102%	$144.7918	$144.79	$144.80	$144.80
Purchase #5	$218.73	6.722%	$233.433	$233.43	$233.45	$233.40
Purchase #6	$19.54	10.260%	$21.5448	$21.54	$21.55	$21.50
Purchase #7	$143.31	10.351%	$158.144	$158.14	$158.15	$158.10
7 purchase totals =	$894.30		$978.7359	$978.71	$978.75	$978.60