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	$154.50	5.808%	$163.4734	$163.47	$163.45	$163.50
Purchase #2	$133.72	7.603%	$143.8867	$143.89	$143.90	$143.90
Purchase #3	$139.27	11.215%	$154.8891	$154.89	$154.90	$154.90
Purchase #4	$64.72	7.645%	$69.6678	$69.67	$69.65	$69.70
Purchase #5	$89.53	12.639%	$100.8457	$100.85	$100.85	$100.80
Purchase #6	$63.93	3.840%	$66.3849	$66.38	$66.40	$66.40
Purchase #7	$215.58	3.324%	$222.7459	$222.75	$222.75	$222.70
7 purchase totals =	$861.25		$921.8935	$921.90	$921.90	$921.90