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	$229.30	4.482%	$239.5772	$239.58	$239.60	$239.60
Purchase #2	$82.92	10.441%	$91.5777	$91.58	$91.60	$91.60
Purchase #3	$185.80	3.602%	$192.4925	$192.49	$192.50	$192.50
Purchase #4	$95.61	10.302%	$105.4597	$105.46	$105.45	$105.50
Purchase #5	$194.47	4.831%	$203.8648	$203.86	$203.85	$203.90
Purchase #6	$21.68	3.649%	$22.4711	$22.47	$22.45	$22.50
Purchase #7	$165.78	6.150%	$175.9755	$175.98	$176.00	$176.00
7 purchase totals =	$975.56		$1,031.4185	$1,031.42	$1,031.45	$1,031.60