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	$70.28	11.777%	$78.5569	$78.56	$78.55	$78.60
Purchase #2	$210.87	3.326%	$217.8835	$217.88	$217.90	$217.90
Purchase #3	$10.44	6.215%	$11.0888	$11.09	$11.10	$11.10
Purchase #4	$175.58	5.206%	$184.7207	$184.72	$184.70	$184.70
Purchase #5	$97.46	9.201%	$106.4273	$106.43	$106.45	$106.40
Purchase #6	$120.81	8.443%	$131.01	$131.01	$131.00	$131.00
Purchase #7	$101.83	12.402%	$114.459	$114.46	$114.45	$114.50
7 purchase totals =	$787.27		$844.1462	$844.15	$844.15	$844.20