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	$38.47	12.381%	$43.233	$43.23	$43.25	$43.20
Purchase #2	$122.74	11.473%	$136.822	$136.82	$136.80	$136.80
Purchase #3	$205.83	4.606%	$215.3105	$215.31	$215.30	$215.30
Purchase #4	$65.65	11.103%	$72.9391	$72.94	$72.95	$72.90
Purchase #5	$39.68	12.678%	$44.7106	$44.71	$44.70	$44.70
Purchase #6	$12.43	5.806%	$13.1517	$13.15	$13.15	$13.20
Purchase #7	$40.87	13.576%	$46.4185	$46.42	$46.40	$46.40
7 purchase totals =	$525.67		$572.5854	$572.58	$572.55	$572.50