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	$20.47	7.802%	$22.0671	$22.07	$22.05	$22.10
Purchase #2	$116.86	3.664%	$121.1418	$121.14	$121.15	$121.10
Purchase #3	$6.43	10.252%	$7.0892	$7.09	$7.10	$7.10
Purchase #4	$250.64	13.449%	$284.3486	$284.35	$284.35	$284.30
Purchase #5	$38.89	5.136%	$40.8874	$40.89	$40.90	$40.90
Purchase #6	$96.70	3.391%	$99.9791	$99.98	$100.00	$100.00
Purchase #7	$98.32	7.366%	$105.5623	$105.56	$105.55	$105.60
7 purchase totals =	$628.31		$681.0755	$681.08	$681.10	$681.10