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	$137.81	9.263%	$150.5753	$150.58	$150.60	$150.60
Purchase #2	$241.56	12.276%	$271.2139	$271.21	$271.20	$271.20
Purchase #3	$180.85	7.237%	$193.9381	$193.94	$193.95	$193.90
Purchase #4	$216.56	8.450%	$234.8593	$234.86	$234.85	$234.90
Purchase #5	$241.61	5.194%	$254.1592	$254.16	$254.15	$254.20
Purchase #6	$127.83	11.682%	$142.7631	$142.76	$142.75	$142.80
Purchase #7	$248.94	10.275%	$274.5186	$274.52	$274.50	$274.50
7 purchase totals =	$1,395.16		$1,522.0275	$1,522.03	$1,522.00	$1,522.10