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	$16.98	6.481%	$18.0805	$18.08	$18.10	$18.10
Purchase #2	$225.62	12.569%	$253.9782	$253.98	$254.00	$254.00
Purchase #3	$237.59	11.650%	$265.2692	$265.27	$265.25	$265.30
Purchase #4	$136.52	5.295%	$143.7487	$143.75	$143.75	$143.70
Purchase #5	$38.70	10.556%	$42.7852	$42.79	$42.80	$42.80
Purchase #6	$195.87	6.265%	$208.1413	$208.14	$208.15	$208.10
Purchase #7	$54.28	13.242%	$61.4678	$61.47	$61.45	$61.50
7 purchase totals =	$905.56		$993.4709	$993.48	$993.50	$993.50