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	$229.32	11.221%	$255.052	$255.05	$255.05	$255.10
Purchase #2	$152.86	3.298%	$157.9013	$157.90	$157.90	$157.90
Purchase #3	$242.48	9.246%	$264.8997	$264.90	$264.90	$264.90
Purchase #4	$115.87	10.348%	$127.8602	$127.86	$127.85	$127.90
Purchase #5	$202.94	3.236%	$209.5071	$209.51	$209.50	$209.50
Purchase #6	$7.34	8.619%	$7.9726	$7.97	$7.95	$8.00
Purchase #7	$38.35	11.545%	$42.7775	$42.78	$42.80	$42.80
7 purchase totals =	$989.16		$1,065.9704	$1,065.97	$1,065.95	$1,066.10