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	$12.89	10.724%	$14.2723	$14.27	$14.25	$14.30
Purchase #2	$140.31	3.222%	$144.8308	$144.83	$144.85	$144.80
Purchase #3	$123.65	12.534%	$139.1483	$139.15	$139.15	$139.10
Purchase #4	$143.97	11.655%	$160.7497	$160.75	$160.75	$160.70
Purchase #5	$172.48	6.139%	$183.0685	$183.07	$183.05	$183.10
Purchase #6	$39.46	3.407%	$40.8044	$40.80	$40.80	$40.80
Purchase #7	$163.90	9.740%	$179.8639	$179.86	$179.85	$179.90
7 purchase totals =	$796.66		$862.7379	$862.73	$862.70	$862.70