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	$30.46	3.220%	$31.4408	$31.44	$31.45	$31.40
Purchase #2	$130.39	5.705%	$137.8287	$137.83	$137.85	$137.80
Purchase #3	$55.41	12.337%	$62.2459	$62.25	$62.25	$62.20
Purchase #4	$36.46	8.594%	$39.5934	$39.59	$39.60	$39.60
Purchase #5	$226.50	10.724%	$250.7899	$250.79	$250.80	$250.80
Purchase #6	$150.72	11.528%	$168.095	$168.10	$168.10	$168.10
Purchase #7	$11.46	4.742%	$12.0034	$12.00	$12.00	$12.00
7 purchase totals =	$641.40		$701.9971	$702.00	$702.05	$701.90