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	$11.71	5.800%	$12.3892	$12.39	$12.40	$12.40
Purchase #2	$111.43	5.850%	$117.9487	$117.95	$117.95	$117.90
Purchase #3	$96.40	3.168%	$99.454	$99.45	$99.45	$99.50
Purchase #4	$141.95	5.844%	$150.2456	$150.25	$150.25	$150.20
Purchase #5	$158.47	12.561%	$178.3754	$178.38	$178.40	$178.40
Purchase #6	$137.28	13.575%	$155.9158	$155.92	$155.90	$155.90
Purchase #7	$87.72	6.620%	$93.5271	$93.53	$93.55	$93.50
7 purchase totals =	$744.96		$807.8558	$807.87	$807.90	$807.80