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	$238.27	10.286%	$262.7785	$262.78	$262.80	$262.80
Purchase #2	$122.97	3.739%	$127.5678	$127.57	$127.55	$127.60
Purchase #3	$202.55	7.482%	$217.7048	$217.70	$217.70	$217.70
Purchase #4	$231.30	10.587%	$255.7877	$255.79	$255.80	$255.80
Purchase #5	$203.56	6.340%	$216.4657	$216.47	$216.45	$216.50
Purchase #6	$60.89	8.356%	$65.978	$65.98	$66.00	$66.00
Purchase #7	$32.50	4.170%	$33.8553	$33.86	$33.85	$33.90
7 purchase totals =	$1,092.04		$1,180.1378	$1,180.15	$1,180.15	$1,180.30