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	$24.84	10.371%	$27.4162	$27.42	$27.40	$27.40
Purchase #2	$129.84	10.238%	$143.133	$143.13	$143.15	$143.10
Purchase #3	$106.86	8.818%	$116.2829	$116.28	$116.30	$116.30
Purchase #4	$140.30	4.724%	$146.9278	$146.93	$146.95	$146.90
Purchase #5	$207.53	8.180%	$224.506	$224.51	$224.50	$224.50
Purchase #6	$201.94	10.827%	$223.804	$223.80	$223.80	$223.80
Purchase #7	$84.70	5.644%	$89.4805	$89.48	$89.50	$89.50
7 purchase totals =	$896.01		$971.5504	$971.55	$971.60	$971.50