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	$36.57	6.292%	$38.871	$38.87	$38.85	$38.90
Purchase #2	$11.59	10.602%	$12.8188	$12.82	$12.80	$12.80
Purchase #3	$198.31	5.297%	$208.8145	$208.81	$208.80	$208.80
Purchase #4	$80.99	11.113%	$89.9904	$89.99	$90.00	$90.00
Purchase #5	$85.25	6.601%	$90.8774	$90.88	$90.90	$90.90
Purchase #6	$24.72	8.312%	$26.7747	$26.77	$26.75	$26.80
Purchase #7	$160.74	6.662%	$171.4485	$171.45	$171.45	$171.40
7 purchase totals =	$598.17		$639.5953	$639.59	$639.55	$639.60