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	$45.47	4.344%	$47.4452	$47.45	$47.45	$47.40
Purchase #2	$87.93	9.299%	$96.1066	$96.11	$96.10	$96.10
Purchase #3	$171.70	3.616%	$177.9087	$177.91	$177.90	$177.90
Purchase #4	$240.52	12.551%	$270.7077	$270.71	$270.70	$270.70
Purchase #5	$105.46	5.258%	$111.0051	$111.01	$111.00	$111.00
Purchase #6	$54.64	8.677%	$59.3811	$59.38	$59.40	$59.40
Purchase #7	$74.32	5.443%	$78.3652	$78.37	$78.35	$78.40
7 purchase totals =	$780.04		$840.9196	$840.94	$840.90	$840.90