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	$79.88	3.747%	$82.8731	$82.87	$82.85	$82.90
Purchase #2	$244.42	12.759%	$275.6055	$275.61	$275.60	$275.60
Purchase #3	$103.79	7.792%	$111.8773	$111.88	$111.90	$111.90
Purchase #4	$8.66	11.863%	$9.6873	$9.69	$9.70	$9.70
Purchase #5	$183.93	10.601%	$203.4284	$203.43	$203.45	$203.40
Purchase #6	$172.52	3.355%	$178.308	$178.31	$178.30	$178.30
Purchase #7	$136.32	13.260%	$154.396	$154.40	$154.40	$154.40
7 purchase totals =	$929.52		$1,016.1756	$1,016.19	$1,016.20	$1,016.20