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	$11.75	8.572%	$12.7572	$12.76	$12.75	$12.80
Purchase #2	$131.37	9.181%	$143.4311	$143.43	$143.45	$143.40
Purchase #3	$239.66	12.535%	$269.7014	$269.70	$269.70	$269.70
Purchase #4	$85.52	8.632%	$92.9021	$92.90	$92.90	$92.90
Purchase #5	$29.45	6.820%	$31.4585	$31.46	$31.45	$31.50
Purchase #6	$92.70	13.428%	$105.1478	$105.15	$105.15	$105.10
Purchase #7	$37.48	10.418%	$41.3847	$41.38	$41.40	$41.40
7 purchase totals =	$627.93		$696.7828	$696.78	$696.80	$696.80