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	$39.83	8.696%	$43.2936	$43.29	$43.30	$43.30
Purchase #2	$103.81	11.360%	$115.6028	$115.60	$115.60	$115.60
Purchase #3	$124.72	12.341%	$140.1117	$140.11	$140.10	$140.10
Purchase #4	$247.79	13.271%	$280.6742	$280.67	$280.65	$280.70
Purchase #5	$119.76	9.640%	$131.3049	$131.30	$131.30	$131.30
Purchase #6	$182.30	5.240%	$191.8525	$191.85	$191.85	$191.90
Purchase #7	$230.97	11.769%	$258.1529	$258.15	$258.15	$258.20
7 purchase totals =	$1,049.18		$1,160.9926	$1,160.97	$1,160.95	$1,161.10