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	$79.54	4.555%	$83.163	$83.16	$83.15	$83.20
Purchase #2	$77.93	7.247%	$83.5776	$83.58	$83.60	$83.60
Purchase #3	$126.60	10.406%	$139.774	$139.77	$139.75	$139.80
Purchase #4	$118.42	4.288%	$123.4978	$123.50	$123.50	$123.50
Purchase #5	$236.87	13.287%	$268.3429	$268.34	$268.35	$268.30
Purchase #6	$78.37	12.105%	$87.8567	$87.86	$87.85	$87.90
Purchase #7	$106.68	5.271%	$112.3031	$112.30	$112.30	$112.30
7 purchase totals =	$824.41		$898.5151	$898.51	$898.50	$898.60