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	$248.99	12.547%	$280.2308	$280.23	$280.25	$280.20
Purchase #2	$141.83	4.189%	$147.7713	$147.77	$147.75	$147.80
Purchase #3	$39.57	9.748%	$43.4273	$43.43	$43.45	$43.40
Purchase #4	$178.95	5.205%	$188.2643	$188.26	$188.25	$188.30
Purchase #5	$95.42	11.358%	$106.2578	$106.26	$106.25	$106.30
Purchase #6	$25.80	10.537%	$28.5185	$28.52	$28.50	$28.50
Purchase #7	$107.70	3.822%	$111.8163	$111.82	$111.80	$111.80
7 purchase totals =	$838.26		$906.2863	$906.29	$906.25	$906.30