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	$127.64	12.699%	$143.849	$143.85	$143.85	$143.80
Purchase #2	$58.86	6.837%	$62.8843	$62.88	$62.90	$62.90
Purchase #3	$68.83	5.711%	$72.7609	$72.76	$72.75	$72.80
Purchase #4	$156.25	10.668%	$172.9188	$172.92	$172.90	$172.90
Purchase #5	$34.31	3.268%	$35.4313	$35.43	$35.45	$35.40
Purchase #6	$84.83	8.130%	$91.7267	$91.73	$91.75	$91.70
Purchase #7	$82.57	3.798%	$85.706	$85.71	$85.70	$85.70
7 purchase totals =	$613.29		$665.2770	$665.28	$665.30	$665.20