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	$53.95	10.853%	$59.8052	$59.81	$59.80	$59.80
Purchase #2	$189.93	13.777%	$216.0967	$216.10	$216.10	$216.10
Purchase #3	$36.60	9.625%	$40.1228	$40.12	$40.10	$40.10
Purchase #4	$59.88	9.328%	$65.4656	$65.47	$65.45	$65.50
Purchase #5	$78.56	8.375%	$85.1394	$85.14	$85.15	$85.10
Purchase #6	$11.90	3.771%	$12.3487	$12.35	$12.35	$12.30
Purchase #7	$141.26	5.754%	$149.3881	$149.39	$149.40	$149.40
7 purchase totals =	$572.08		$628.3665	$628.38	$628.35	$628.30