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	$74.58	13.808%	$84.878	$84.88	$84.90	$84.90
Purchase #2	$217.99	7.251%	$233.7965	$233.80	$233.80	$233.80
Purchase #3	$126.27	4.178%	$131.5456	$131.55	$131.55	$131.50
Purchase #4	$144.48	13.647%	$164.1972	$164.20	$164.20	$164.20
Purchase #5	$41.28	10.368%	$45.5599	$45.56	$45.55	$45.60
Purchase #6	$168.43	6.828%	$179.9304	$179.93	$179.95	$179.90
Purchase #7	$132.91	8.766%	$144.5609	$144.56	$144.55	$144.60
7 purchase totals =	$905.94		$984.4685	$984.48	$984.50	$984.50