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	$97.32	8.303%	$105.4005	$105.40	$105.40	$105.40
Purchase #2	$42.27	5.467%	$44.5809	$44.58	$44.60	$44.60
Purchase #3	$220.78	4.675%	$231.1015	$231.10	$231.10	$231.10
Purchase #4	$107.99	13.759%	$122.8483	$122.85	$122.85	$122.80
Purchase #5	$136.84	3.699%	$141.9017	$141.90	$141.90	$141.90
Purchase #6	$83.96	7.703%	$90.4274	$90.43	$90.45	$90.40
Purchase #7	$157.60	4.286%	$164.3547	$164.35	$164.35	$164.40
7 purchase totals =	$846.76		$900.6150	$900.61	$900.65	$900.60