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	$116.55	6.271%	$123.8589	$123.86	$123.85	$123.90
Purchase #2	$80.26	10.585%	$88.7555	$88.76	$88.75	$88.80
Purchase #3	$210.49	11.419%	$234.5259	$234.53	$234.55	$234.50
Purchase #4	$205.51	13.856%	$233.9855	$233.99	$234.00	$234.00
Purchase #5	$171.46	5.104%	$180.2113	$180.21	$180.20	$180.20
Purchase #6	$38.66	5.477%	$40.7774	$40.78	$40.80	$40.80
Purchase #7	$59.64	13.428%	$67.6485	$67.65	$67.65	$67.60
7 purchase totals =	$882.57		$969.7630	$969.78	$969.80	$969.80