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	$11.56	7.493%	$12.4262	$12.43	$12.45	$12.40
Purchase #2	$21.46	13.203%	$24.2934	$24.29	$24.30	$24.30
Purchase #3	$76.82	13.108%	$86.8896	$86.89	$86.90	$86.90
Purchase #4	$198.75	5.457%	$209.5958	$209.60	$209.60	$209.60
Purchase #5	$233.98	8.794%	$254.5562	$254.56	$254.55	$254.60
Purchase #6	$28.26	5.325%	$29.7648	$29.76	$29.75	$29.80
Purchase #7	$73.73	6.241%	$78.3315	$78.33	$78.35	$78.30
7 purchase totals =	$644.56		$695.8575	$695.86	$695.90	$695.90