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	$247.47	13.374%	$280.5666	$280.57	$280.55	$280.60
Purchase #2	$189.45	10.522%	$209.3839	$209.38	$209.40	$209.40
Purchase #3	$109.70	7.652%	$118.0942	$118.09	$118.10	$118.10
Purchase #4	$146.83	12.202%	$164.7462	$164.75	$164.75	$164.70
Purchase #5	$12.52	9.592%	$13.7209	$13.72	$13.70	$13.70
Purchase #6	$75.78	3.440%	$78.3868	$78.39	$78.40	$78.40
Purchase #7	$211.40	8.177%	$228.6862	$228.69	$228.70	$228.70
7 purchase totals =	$993.15		$1,093.5848	$1,093.59	$1,093.60	$1,093.60