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	$250.64	9.776%	$275.1426	$275.14	$275.15	$275.10
Purchase #2	$176.89	8.252%	$191.487	$191.49	$191.50	$191.50
Purchase #3	$20.31	6.147%	$21.5585	$21.56	$21.55	$21.60
Purchase #4	$109.61	11.378%	$122.0814	$122.08	$122.10	$122.10
Purchase #5	$135.98	5.186%	$143.0319	$143.03	$143.05	$143.00
Purchase #6	$206.93	12.662%	$233.1315	$233.13	$233.15	$233.10
Purchase #7	$102.68	10.777%	$113.7458	$113.75	$113.75	$113.70
7 purchase totals =	$1,003.04		$1,100.1787	$1,100.18	$1,100.25	$1,100.10