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	$24.45	11.624%	$27.2921	$27.29	$27.30	$27.30
Purchase #2	$195.45	6.553%	$208.2578	$208.26	$208.25	$208.30
Purchase #3	$20.38	4.841%	$21.3666	$21.37	$21.35	$21.40
Purchase #4	$104.45	6.368%	$111.1014	$111.10	$111.10	$111.10
Purchase #5	$150.78	7.846%	$162.6102	$162.61	$162.60	$162.60
Purchase #6	$62.51	4.134%	$65.0942	$65.09	$65.10	$65.10
Purchase #7	$9.90	3.859%	$10.282	$10.28	$10.30	$10.30
7 purchase totals =	$567.92		$606.0043	$606.00	$606.00	$606.10