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	$21.86	11.810%	$24.4417	$24.44	$24.45	$24.40
Purchase #2	$90.60	11.736%	$101.2328	$101.23	$101.25	$101.20
Purchase #3	$41.80	13.680%	$47.5182	$47.52	$47.50	$47.50
Purchase #4	$103.37	10.615%	$114.3427	$114.34	$114.35	$114.30
Purchase #5	$41.81	8.554%	$45.3864	$45.39	$45.40	$45.40
Purchase #6	$40.49	11.516%	$45.1528	$45.15	$45.15	$45.20
Purchase #7	$37.86	3.390%	$39.1435	$39.14	$39.15	$39.10
7 purchase totals =	$377.79		$417.2181	$417.21	$417.25	$417.10