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	$9.38	10.869%	$10.3995	$10.40	$10.40	$10.40
Purchase #2	$153.74	13.267%	$174.1367	$174.14	$174.15	$174.10
Purchase #3	$47.27	4.684%	$49.4841	$49.48	$49.50	$49.50
Purchase #4	$229.36	11.188%	$255.0208	$255.02	$255.00	$255.00
Purchase #5	$215.94	9.619%	$236.7113	$236.71	$236.70	$236.70
Purchase #6	$147.85	4.168%	$154.0124	$154.01	$154.00	$154.00
Purchase #7	$88.99	11.400%	$99.1349	$99.13	$99.15	$99.10
7 purchase totals =	$892.53		$978.8997	$978.89	$978.90	$978.80