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	$145.82	9.707%	$159.9747	$159.97	$159.95	$160.00
Purchase #2	$67.36	7.864%	$72.6572	$72.66	$72.65	$72.70
Purchase #3	$17.32	5.593%	$18.2887	$18.29	$18.30	$18.30
Purchase #4	$74.78	8.405%	$81.0653	$81.07	$81.05	$81.10
Purchase #5	$38.34	13.365%	$43.4641	$43.46	$43.45	$43.50
Purchase #6	$224.60	9.846%	$246.7141	$246.71	$246.70	$246.70
Purchase #7	$145.55	13.267%	$164.8601	$164.86	$164.85	$164.90
7 purchase totals =	$713.77		$787.0242	$787.02	$786.95	$787.20