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	$12.91	5.621%	$13.6357	$13.64	$13.65	$13.60
Purchase #2	$148.27	11.210%	$164.8911	$164.89	$164.90	$164.90
Purchase #3	$78.32	5.271%	$82.4482	$82.45	$82.45	$82.40
Purchase #4	$202.89	11.680%	$226.5876	$226.59	$226.60	$226.60
Purchase #5	$141.90	12.558%	$159.7198	$159.72	$159.70	$159.70
Purchase #6	$25.59	4.837%	$26.8278	$26.83	$26.85	$26.80
Purchase #7	$138.92	6.496%	$147.9442	$147.94	$147.95	$147.90
7 purchase totals =	$748.80		$822.0544	$822.06	$822.10	$821.90