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	$34.48	8.688%	$37.4756	$37.48	$37.50	$37.50
Purchase #2	$217.62	7.352%	$233.6194	$233.62	$233.60	$233.60
Purchase #3	$13.98	9.296%	$15.2796	$15.28	$15.30	$15.30
Purchase #4	$75.68	3.396%	$78.2501	$78.25	$78.25	$78.30
Purchase #5	$192.32	9.612%	$210.8058	$210.81	$210.80	$210.80
Purchase #6	$152.68	11.319%	$169.9618	$169.96	$169.95	$170.00
Purchase #7	$246.98	13.545%	$280.4334	$280.43	$280.45	$280.40
7 purchase totals =	$933.74		$1,025.8257	$1,025.83	$1,025.85	$1,025.90