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	$159.35	5.313%	$167.8163	$167.82	$167.80	$167.80
Purchase #2	$153.58	3.182%	$158.4669	$158.47	$158.45	$158.50
Purchase #3	$96.95	10.606%	$107.2325	$107.23	$107.25	$107.20
Purchase #4	$18.98	4.386%	$19.8125	$19.81	$19.80	$19.80
Purchase #5	$93.96	8.559%	$102.002	$102.00	$102.00	$102.00
Purchase #6	$123.46	13.515%	$140.1456	$140.15	$140.15	$140.10
Purchase #7	$119.28	3.504%	$123.4596	$123.46	$123.45	$123.50
7 purchase totals =	$765.56		$818.9354	$818.94	$818.90	$818.90