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	$220.74	13.618%	$250.8004	$250.80	$250.80	$250.80
Purchase #2	$154.59	12.469%	$173.8658	$173.87	$173.85	$173.90
Purchase #3	$128.67	4.356%	$134.2749	$134.27	$134.25	$134.30
Purchase #4	$57.81	7.271%	$62.0134	$62.01	$62.00	$62.00
Purchase #5	$101.90	3.585%	$105.5531	$105.55	$105.55	$105.60
Purchase #6	$63.66	13.859%	$72.4826	$72.48	$72.50	$72.50
Purchase #7	$154.81	10.133%	$170.4969	$170.50	$170.50	$170.50
7 purchase totals =	$882.18		$969.4871	$969.48	$969.45	$969.60