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	$59.72	11.827%	$66.7831	$66.78	$66.80	$66.80
Purchase #2	$248.60	4.128%	$258.8622	$258.86	$258.85	$258.90
Purchase #3	$29.60	13.223%	$33.514	$33.51	$33.50	$33.50
Purchase #4	$214.82	9.626%	$235.4986	$235.50	$235.50	$235.50
Purchase #5	$136.51	4.204%	$142.2489	$142.25	$142.25	$142.20
Purchase #6	$199.97	11.473%	$222.9126	$222.91	$222.90	$222.90
Purchase #7	$17.67	9.409%	$19.3326	$19.33	$19.35	$19.30
7 purchase totals =	$906.89		$979.1520	$979.14	$979.15	$979.10