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	$59.42	13.571%	$67.4839	$67.48	$67.50	$67.50
Purchase #2	$246.44	13.680%	$280.153	$280.15	$280.15	$280.20
Purchase #3	$164.91	11.226%	$183.4228	$183.42	$183.40	$183.40
Purchase #4	$19.58	10.742%	$21.6833	$21.68	$21.70	$21.70
Purchase #5	$181.87	7.763%	$195.9886	$195.99	$196.00	$196.00
Purchase #6	$104.33	8.584%	$113.2857	$113.29	$113.30	$113.30
Purchase #7	$38.64	4.782%	$40.4878	$40.49	$40.50	$40.50
7 purchase totals =	$815.19		$902.5051	$902.50	$902.55	$902.60