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	$184.68	8.294%	$199.9974	$200.00	$200.00	$200.00
Purchase #2	$36.44	11.342%	$40.573	$40.57	$40.55	$40.60
Purchase #3	$129.43	7.789%	$139.5113	$139.51	$139.50	$139.50
Purchase #4	$53.26	11.597%	$59.4366	$59.44	$59.45	$59.40
Purchase #5	$59.43	5.201%	$62.521	$62.52	$62.50	$62.50
Purchase #6	$78.32	8.436%	$84.9271	$84.93	$84.95	$84.90
Purchase #7	$75.38	9.337%	$82.4182	$82.42	$82.40	$82.40
7 purchase totals =	$616.94		$669.3846	$669.39	$669.35	$669.30