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	$30.51	9.679%	$33.4631	$33.46	$33.45	$33.50
Purchase #2	$29.90	6.302%	$31.7843	$31.78	$31.80	$31.80
Purchase #3	$216.29	6.561%	$230.4808	$230.48	$230.50	$230.50
Purchase #4	$51.25	4.189%	$53.3969	$53.40	$53.40	$53.40
Purchase #5	$51.90	4.863%	$54.4239	$54.42	$54.40	$54.40
Purchase #6	$47.81	9.770%	$52.481	$52.48	$52.50	$52.50
Purchase #7	$39.55	6.403%	$42.0824	$42.08	$42.10	$42.10
7 purchase totals =	$467.21		$498.1124	$498.10	$498.15	$498.20