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	$11.85	7.874%	$12.7831	$12.78	$12.80	$12.80
Purchase #2	$183.66	11.861%	$205.4439	$205.44	$205.45	$205.40
Purchase #3	$54.74	11.399%	$60.9798	$60.98	$61.00	$61.00
Purchase #4	$81.25	11.548%	$90.6328	$90.63	$90.65	$90.60
Purchase #5	$38.89	6.858%	$41.5571	$41.56	$41.55	$41.60
Purchase #6	$81.64	9.862%	$89.6913	$89.69	$89.70	$89.70
Purchase #7	$30.34	5.329%	$31.9568	$31.96	$31.95	$32.00
7 purchase totals =	$482.37		$533.0448	$533.04	$533.10	$533.10