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	$229.83	12.326%	$258.1588	$258.16	$258.15	$258.20
Purchase #2	$246.88	13.615%	$280.4927	$280.49	$280.50	$280.50
Purchase #3	$155.38	10.389%	$171.5224	$171.52	$171.50	$171.50
Purchase #4	$117.97	8.558%	$128.0659	$128.07	$128.05	$128.10
Purchase #5	$219.92	10.218%	$242.3914	$242.39	$242.40	$242.40
Purchase #6	$54.75	12.226%	$61.4437	$61.44	$61.45	$61.40
Purchase #7	$142.68	11.286%	$158.7829	$158.78	$158.80	$158.80
7 purchase totals =	$1,167.41		$1,300.8578	$1,300.85	$1,300.85	$1,300.90