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	$117.47	8.475%	$127.4256	$127.43	$127.45	$127.40
Purchase #2	$142.86	13.253%	$161.7932	$161.79	$161.80	$161.80
Purchase #3	$121.55	12.322%	$136.5274	$136.53	$136.55	$136.50
Purchase #4	$85.79	9.207%	$93.6887	$93.69	$93.70	$93.70
Purchase #5	$155.88	8.691%	$169.4275	$169.43	$169.45	$169.40
Purchase #6	$113.67	11.765%	$127.0433	$127.04	$127.05	$127.00
Purchase #7	$227.60	12.550%	$256.1638	$256.16	$256.15	$256.20
7 purchase totals =	$964.82		$1,072.0695	$1,072.07	$1,072.15	$1,072.00