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	$160.51	5.172%	$168.8116	$168.81	$168.80	$168.80
Purchase #2	$234.70	4.776%	$245.9093	$245.91	$245.90	$245.90
Purchase #3	$196.93	4.147%	$205.0967	$205.10	$205.10	$205.10
Purchase #4	$139.68	10.676%	$154.5922	$154.59	$154.60	$154.60
Purchase #5	$78.51	4.446%	$82.0006	$82.00	$82.00	$82.00
Purchase #6	$234.35	9.191%	$255.8891	$255.89	$255.90	$255.90
Purchase #7	$71.77	6.728%	$76.5987	$76.60	$76.60	$76.60
7 purchase totals =	$1,116.45		$1,188.8982	$1,188.90	$1,188.90	$1,188.90