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	$27.79	7.338%	$29.8292	$29.83	$29.85	$29.80
Purchase #2	$100.80	3.333%	$104.1597	$104.16	$104.15	$104.20
Purchase #3	$83.99	10.600%	$92.8929	$92.89	$92.90	$92.90
Purchase #4	$36.28	11.516%	$40.458	$40.46	$40.45	$40.50
Purchase #5	$99.41	13.191%	$112.5232	$112.52	$112.50	$112.50
Purchase #6	$178.79	13.746%	$203.3665	$203.37	$203.35	$203.40
Purchase #7	$191.50	13.125%	$216.6344	$216.63	$216.65	$216.60
7 purchase totals =	$718.56		$799.8639	$799.86	$799.85	$799.90