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	$206.61	12.724%	$232.8991	$232.90	$232.90	$232.90
Purchase #2	$59.68	13.408%	$67.6819	$67.68	$67.70	$67.70
Purchase #3	$114.38	3.710%	$118.6235	$118.62	$118.60	$118.60
Purchase #4	$151.33	4.584%	$158.267	$158.27	$158.25	$158.30
Purchase #5	$231.61	3.839%	$240.5015	$240.50	$240.50	$240.50
Purchase #6	$44.89	11.411%	$50.0124	$50.01	$50.00	$50.00
Purchase #7	$6.92	13.804%	$7.8752	$7.88	$7.90	$7.90
7 purchase totals =	$815.42		$875.8606	$875.86	$875.85	$875.90