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	$232.62	9.786%	$255.3842	$255.38	$255.40	$255.40
Purchase #2	$247.37	13.314%	$280.3048	$280.30	$280.30	$280.30
Purchase #3	$153.82	13.595%	$174.7318	$174.73	$174.75	$174.70
Purchase #4	$45.70	4.495%	$47.7542	$47.75	$47.75	$47.80
Purchase #5	$164.38	12.688%	$185.2365	$185.24	$185.25	$185.20
Purchase #6	$249.85	8.800%	$271.8368	$271.84	$271.85	$271.80
Purchase #7	$12.28	7.176%	$13.1612	$13.16	$13.15	$13.20
7 purchase totals =	$1,106.02		$1,228.4095	$1,228.40	$1,228.45	$1,228.40