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	$57.91	13.659%	$65.8199	$65.82	$65.80	$65.80
Purchase #2	$62.26	11.587%	$69.4741	$69.47	$69.45	$69.50
Purchase #3	$237.42	7.667%	$255.623	$255.62	$255.60	$255.60
Purchase #4	$75.89	7.304%	$81.433	$81.43	$81.45	$81.40
Purchase #5	$155.98	3.173%	$160.9292	$160.93	$160.95	$160.90
Purchase #6	$161.42	6.724%	$172.2739	$172.27	$172.25	$172.30
Purchase #7	$175.80	5.480%	$185.4338	$185.43	$185.45	$185.40
7 purchase totals =	$926.68		$990.9869	$990.97	$990.95	$990.90