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	$38.78	6.197%	$41.1832	$41.18	$41.20	$41.20
Purchase #2	$16.97	8.746%	$18.4542	$18.45	$18.45	$18.50
Purchase #3	$80.38	12.791%	$90.6614	$90.66	$90.65	$90.70
Purchase #4	$50.96	11.668%	$56.906	$56.91	$56.90	$56.90
Purchase #5	$175.69	4.602%	$183.7753	$183.78	$183.80	$183.80
Purchase #6	$156.80	9.440%	$171.6019	$171.60	$171.60	$171.60
Purchase #7	$65.83	12.821%	$74.2701	$74.27	$74.25	$74.30
7 purchase totals =	$585.41		$636.8521	$636.85	$636.85	$637.00