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	$192.51	13.627%	$218.7433	$218.74	$218.75	$218.70
Purchase #2	$178.55	3.123%	$184.1261	$184.13	$184.15	$184.10
Purchase #3	$199.60	8.130%	$215.8275	$215.83	$215.85	$215.80
Purchase #4	$128.33	8.334%	$139.025	$139.03	$139.05	$139.00
Purchase #5	$119.32	3.779%	$123.8291	$123.83	$123.85	$123.80
Purchase #6	$31.63	10.109%	$34.8275	$34.83	$34.85	$34.80
Purchase #7	$38.46	11.715%	$42.9656	$42.97	$42.95	$43.00
7 purchase totals =	$888.40		$959.3441	$959.36	$959.45	$959.20