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	$19.83	5.389%	$20.8986	$20.90	$20.90	$20.90
Purchase #2	$9.94	6.264%	$10.5626	$10.56	$10.55	$10.60
Purchase #3	$31.41	10.401%	$34.677	$34.68	$34.70	$34.70
Purchase #4	$36.34	11.716%	$40.5976	$40.60	$40.60	$40.60
Purchase #5	$234.71	11.866%	$262.5607	$262.56	$262.55	$262.60
Purchase #6	$205.76	12.665%	$231.8195	$231.82	$231.80	$231.80
Purchase #7	$176.81	12.851%	$199.5319	$199.53	$199.55	$199.50
7 purchase totals =	$714.80		$800.6479	$800.65	$800.65	$800.70