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	$18.58	3.119%	$19.1595	$19.16	$19.15	$19.20
Purchase #2	$136.75	5.545%	$144.3328	$144.33	$144.35	$144.30
Purchase #3	$87.56	12.771%	$98.7423	$98.74	$98.75	$98.70
Purchase #4	$141.52	3.558%	$146.5553	$146.56	$146.55	$146.60
Purchase #5	$151.37	10.217%	$166.8355	$166.84	$166.85	$166.80
Purchase #6	$166.69	13.644%	$189.4332	$189.43	$189.45	$189.40
Purchase #7	$83.75	13.338%	$94.9206	$94.92	$94.90	$94.90
7 purchase totals =	$786.22		$859.9792	$859.98	$860.00	$859.90