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	$16.57	12.783%	$18.6881	$18.69	$18.70	$18.70
Purchase #2	$182.62	7.581%	$196.4644	$196.46	$196.45	$196.50
Purchase #3	$31.59	11.261%	$35.1473	$35.15	$35.15	$35.10
Purchase #4	$18.40	12.504%	$20.7007	$20.70	$20.70	$20.70
Purchase #5	$154.66	8.535%	$167.8602	$167.86	$167.85	$167.90
Purchase #6	$89.83	11.412%	$100.0814	$100.08	$100.10	$100.10
Purchase #7	$84.90	12.680%	$95.6653	$95.67	$95.65	$95.70
7 purchase totals =	$578.57		$634.6074	$634.61	$634.60	$634.70