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	$224.72	12.789%	$253.4594	$253.46	$253.45	$253.50
Purchase #2	$212.77	10.371%	$234.8364	$234.84	$234.85	$234.80
Purchase #3	$171.39	11.523%	$191.1393	$191.14	$191.15	$191.10
Purchase #4	$34.66	9.810%	$38.0601	$38.06	$38.05	$38.10
Purchase #5	$17.32	12.149%	$19.4242	$19.42	$19.40	$19.40
Purchase #6	$143.37	4.353%	$149.6109	$149.61	$149.60	$149.60
Purchase #7	$148.58	10.382%	$164.0056	$164.01	$164.00	$164.00
7 purchase totals =	$952.81		$1,050.5359	$1,050.54	$1,050.50	$1,050.50