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	$233.32	12.422%	$262.303	$262.30	$262.30	$262.30
Purchase #2	$159.89	7.193%	$171.3909	$171.39	$171.40	$171.40
Purchase #3	$249.32	8.699%	$271.0083	$271.01	$271.00	$271.00
Purchase #4	$85.27	7.429%	$91.6047	$91.60	$91.60	$91.60
Purchase #5	$88.56	3.340%	$91.5179	$91.52	$91.50	$91.50
Purchase #6	$159.75	11.843%	$178.6692	$178.67	$178.65	$178.70
Purchase #7	$94.61	8.246%	$102.4115	$102.41	$102.40	$102.40
7 purchase totals =	$1,070.72		$1,168.9055	$1,168.90	$1,168.85	$1,168.90