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	$78.59	9.861%	$86.3398	$86.34	$86.35	$86.30
Purchase #2	$135.41	6.277%	$143.9097	$143.91	$143.90	$143.90
Purchase #3	$113.76	5.239%	$119.7199	$119.72	$119.70	$119.70
Purchase #4	$72.77	11.514%	$81.1487	$81.15	$81.15	$81.10
Purchase #5	$42.39	9.725%	$46.5124	$46.51	$46.50	$46.50
Purchase #6	$42.89	11.777%	$47.9412	$47.94	$47.95	$47.90
Purchase #7	$158.78	5.533%	$167.5653	$167.57	$167.55	$167.60
7 purchase totals =	$644.59		$693.1370	$693.14	$693.10	$693.00