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	$240.80	6.438%	$256.3027	$256.30	$256.30	$256.30
Purchase #2	$154.96	9.147%	$169.1342	$169.13	$169.15	$169.10
Purchase #3	$143.47	9.739%	$157.4425	$157.44	$157.45	$157.40
Purchase #4	$200.83	12.196%	$225.3232	$225.32	$225.30	$225.30
Purchase #5	$42.43	9.770%	$46.5754	$46.58	$46.60	$46.60
Purchase #6	$32.80	4.674%	$34.3331	$34.33	$34.35	$34.30
Purchase #7	$74.25	5.184%	$78.0991	$78.10	$78.10	$78.10
7 purchase totals =	$889.54		$967.2102	$967.20	$967.25	$967.10