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	$231.53	3.565%	$239.784	$239.78	$239.80	$239.80
Purchase #2	$169.43	12.188%	$190.0801	$190.08	$190.10	$190.10
Purchase #3	$6.53	11.553%	$7.2844	$7.28	$7.30	$7.30
Purchase #4	$178.45	3.380%	$184.4816	$184.48	$184.50	$184.50
Purchase #5	$230.96	12.513%	$259.86	$259.86	$259.85	$259.90
Purchase #6	$127.40	11.763%	$142.3861	$142.39	$142.40	$142.40
Purchase #7	$69.59	3.869%	$72.2824	$72.28	$72.30	$72.30
7 purchase totals =	$1,013.89		$1,096.1586	$1,096.15	$1,096.25	$1,096.30