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	$226.85	12.615%	$255.4671	$255.47	$255.45	$255.50
Purchase #2	$100.82	13.315%	$114.2442	$114.24	$114.25	$114.20
Purchase #3	$59.51	8.210%	$64.3958	$64.40	$64.40	$64.40
Purchase #4	$129.43	4.262%	$134.9463	$134.95	$134.95	$134.90
Purchase #5	$86.39	5.298%	$90.9669	$90.97	$90.95	$91.00
Purchase #6	$125.31	5.704%	$132.4577	$132.46	$132.45	$132.50
Purchase #7	$80.27	8.302%	$86.934	$86.93	$86.95	$86.90
7 purchase totals =	$808.58		$879.4120	$879.42	$879.40	$879.40