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	$30.64	5.667%	$32.3764	$32.38	$32.40	$32.40
Purchase #2	$63.37	4.683%	$66.3376	$66.34	$66.35	$66.30
Purchase #3	$10.32	12.315%	$11.5909	$11.59	$11.60	$11.60
Purchase #4	$129.57	7.250%	$138.9638	$138.96	$138.95	$139.00
Purchase #5	$35.91	4.416%	$37.4958	$37.50	$37.50	$37.50
Purchase #6	$212.80	13.309%	$241.1216	$241.12	$241.10	$241.10
Purchase #7	$158.70	9.403%	$173.6226	$173.62	$173.60	$173.60
7 purchase totals =	$641.31		$701.5087	$701.51	$701.50	$701.50