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	$76.31	5.238%	$80.3071	$80.31	$80.30	$80.30
Purchase #2	$12.41	11.411%	$13.8261	$13.83	$13.85	$13.80
Purchase #3	$13.48	10.702%	$14.9226	$14.92	$14.90	$14.90
Purchase #4	$144.35	12.293%	$162.0949	$162.09	$162.10	$162.10
Purchase #5	$65.78	8.362%	$71.2805	$71.28	$71.30	$71.30
Purchase #6	$70.70	13.820%	$80.4707	$80.47	$80.45	$80.50
Purchase #7	$156.60	10.587%	$173.1792	$173.18	$173.20	$173.20
7 purchase totals =	$539.63		$596.0811	$596.08	$596.10	$596.10