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	$38.42	5.181%	$40.4105	$40.41	$40.40	$40.40
Purchase #2	$209.40	6.714%	$223.4591	$223.46	$223.45	$223.50
Purchase #3	$205.70	12.592%	$231.6017	$231.60	$231.60	$231.60
Purchase #4	$179.54	9.425%	$196.4616	$196.46	$196.45	$196.50
Purchase #5	$110.28	7.381%	$118.4198	$118.42	$118.40	$118.40
Purchase #6	$85.74	7.524%	$92.1911	$92.19	$92.20	$92.20
Purchase #7	$160.31	8.509%	$173.9508	$173.95	$173.95	$174.00
7 purchase totals =	$989.39		$1,076.4946	$1,076.49	$1,076.45	$1,076.60