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	$128.49	3.128%	$132.5092	$132.51	$132.50	$132.50
Purchase #2	$186.83	10.270%	$206.0174	$206.02	$206.00	$206.00
Purchase #3	$140.71	5.523%	$148.4814	$148.48	$148.50	$148.50
Purchase #4	$112.47	6.769%	$120.0831	$120.08	$120.10	$120.10
Purchase #5	$34.96	11.229%	$38.8857	$38.89	$38.90	$38.90
Purchase #6	$129.89	11.252%	$144.5052	$144.51	$144.50	$144.50
Purchase #7	$51.25	10.319%	$56.5385	$56.54	$56.55	$56.50
7 purchase totals =	$784.60		$847.0205	$847.03	$847.05	$847.00