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	$233.76	9.492%	$255.9485	$255.95	$255.95	$255.90
Purchase #2	$204.70	8.179%	$221.4424	$221.44	$221.45	$221.40
Purchase #3	$91.82	6.387%	$97.6845	$97.68	$97.70	$97.70
Purchase #4	$86.35	4.418%	$90.1649	$90.16	$90.15	$90.20
Purchase #5	$46.59	12.309%	$52.3248	$52.32	$52.30	$52.30
Purchase #6	$155.30	13.682%	$176.5481	$176.55	$176.55	$176.50
Purchase #7	$48.83	6.802%	$52.1514	$52.15	$52.15	$52.20
7 purchase totals =	$867.35		$946.2646	$946.25	$946.25	$946.20