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	$17.65	5.816%	$18.6765	$18.68	$18.70	$18.70
Purchase #2	$108.37	13.759%	$123.2806	$123.28	$123.30	$123.30
Purchase #3	$156.48	10.509%	$172.9245	$172.92	$172.90	$172.90
Purchase #4	$111.93	13.540%	$127.0853	$127.09	$127.10	$127.10
Purchase #5	$226.32	6.379%	$240.757	$240.76	$240.75	$240.80
Purchase #6	$31.44	12.334%	$35.3178	$35.32	$35.30	$35.30
Purchase #7	$112.41	10.619%	$124.3468	$124.35	$124.35	$124.30
7 purchase totals =	$764.60		$842.3885	$842.40	$842.40	$842.40