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	$64.94	10.622%	$71.8379	$71.84	$71.85	$71.80
Purchase #2	$130.38	6.780%	$139.2198	$139.22	$139.20	$139.20
Purchase #3	$78.32	12.221%	$87.8915	$87.89	$87.90	$87.90
Purchase #4	$208.70	6.164%	$221.5643	$221.56	$221.55	$221.60
Purchase #5	$133.42	4.534%	$139.4693	$139.47	$139.45	$139.50
Purchase #6	$168.77	9.179%	$184.2614	$184.26	$184.25	$184.30
Purchase #7	$133.26	13.832%	$151.6925	$151.69	$151.70	$151.70
7 purchase totals =	$917.79		$995.9367	$995.93	$995.90	$996.00