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	$6.59	8.493%	$7.1497	$7.15	$7.15	$7.10
Purchase #2	$241.58	13.510%	$274.2175	$274.22	$274.20	$274.20
Purchase #3	$199.83	10.557%	$220.9261	$220.93	$220.95	$220.90
Purchase #4	$171.55	4.109%	$178.599	$178.60	$178.60	$178.60
Purchase #5	$221.31	3.202%	$228.3963	$228.40	$228.40	$228.40
Purchase #6	$27.70	11.724%	$30.9475	$30.95	$30.95	$30.90
Purchase #7	$72.89	7.660%	$78.4734	$78.47	$78.45	$78.50
7 purchase totals =	$941.45		$1,018.7095	$1,018.72	$1,018.70	$1,018.60