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	$197.69	8.635%	$214.7605	$214.76	$214.75	$214.80
Purchase #2	$51.83	12.119%	$58.1113	$58.11	$58.10	$58.10
Purchase #3	$213.25	9.627%	$233.7796	$233.78	$233.80	$233.80
Purchase #4	$70.75	11.316%	$78.7561	$78.76	$78.75	$78.80
Purchase #5	$93.56	11.706%	$104.5121	$104.51	$104.50	$104.50
Purchase #6	$136.32	5.325%	$143.579	$143.58	$143.60	$143.60
Purchase #7	$40.69	11.698%	$45.4499	$45.45	$45.45	$45.40
7 purchase totals =	$804.09		$878.9485	$878.95	$878.95	$879.00