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	$131.66	9.627%	$144.3349	$144.33	$144.35	$144.30
Purchase #2	$150.86	8.280%	$163.3512	$163.35	$163.35	$163.40
Purchase #3	$235.35	12.756%	$265.3712	$265.37	$265.35	$265.40
Purchase #4	$200.54	13.609%	$227.8315	$227.83	$227.85	$227.80
Purchase #5	$144.31	4.511%	$150.8198	$150.82	$150.80	$150.80
Purchase #6	$151.96	11.802%	$169.8943	$169.89	$169.90	$169.90
Purchase #7	$46.49	8.121%	$50.2655	$50.27	$50.25	$50.30
7 purchase totals =	$1,061.17		$1,171.8684	$1,171.86	$1,171.85	$1,171.90