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	$142.52	10.778%	$157.8808	$157.88	$157.90	$157.90
Purchase #2	$78.73	5.345%	$82.9381	$82.94	$82.95	$82.90
Purchase #3	$201.78	12.250%	$226.4981	$226.50	$226.50	$226.50
Purchase #4	$53.29	8.437%	$57.7861	$57.79	$57.80	$57.80
Purchase #5	$173.88	9.188%	$189.8561	$189.86	$189.85	$189.90
Purchase #6	$101.29	4.576%	$105.925	$105.93	$105.95	$105.90
Purchase #7	$132.85	8.364%	$143.9616	$143.96	$143.95	$144.00
7 purchase totals =	$884.34		$964.8458	$964.86	$964.90	$964.90