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	$41.46	12.225%	$46.5285	$46.53	$46.55	$46.50
Purchase #2	$136.85	5.801%	$144.7887	$144.79	$144.80	$144.80
Purchase #3	$198.42	4.757%	$207.8588	$207.86	$207.85	$207.90
Purchase #4	$71.36	9.382%	$78.055	$78.06	$78.05	$78.10
Purchase #5	$220.57	8.789%	$239.9559	$239.96	$239.95	$240.00
Purchase #6	$54.32	11.495%	$60.5641	$60.56	$60.55	$60.60
Purchase #7	$68.63	5.776%	$72.5941	$72.59	$72.60	$72.60
7 purchase totals =	$791.61		$850.3451	$850.35	$850.35	$850.50