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	$50.94	9.508%	$55.7834	$55.78	$55.80	$55.80
Purchase #2	$51.70	6.438%	$55.0284	$55.03	$55.05	$55.00
Purchase #3	$155.94	6.540%	$166.1385	$166.14	$166.15	$166.10
Purchase #4	$235.81	12.871%	$266.1611	$266.16	$266.15	$266.20
Purchase #5	$36.97	10.620%	$40.8962	$40.90	$40.90	$40.90
Purchase #6	$178.56	12.429%	$200.7532	$200.75	$200.75	$200.80
Purchase #7	$166.56	11.291%	$185.3663	$185.37	$185.35	$185.40
7 purchase totals =	$876.48		$970.1271	$970.13	$970.15	$970.20