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	$94.30	6.744%	$100.6596	$100.66	$100.65	$100.70
Purchase #2	$131.61	10.613%	$145.5778	$145.58	$145.60	$145.60
Purchase #3	$38.29	12.865%	$43.216	$43.22	$43.20	$43.20
Purchase #4	$232.67	11.714%	$259.925	$259.93	$259.95	$259.90
Purchase #5	$203.74	10.298%	$224.7211	$224.72	$224.70	$224.70
Purchase #6	$30.46	6.824%	$32.5386	$32.54	$32.55	$32.50
Purchase #7	$74.30	5.454%	$78.3523	$78.35	$78.35	$78.40
7 purchase totals =	$805.37		$884.9904	$885.00	$885.00	$885.00