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	$240.66	8.870%	$262.0065	$262.01	$262.00	$262.00
Purchase #2	$146.93	6.437%	$156.3879	$156.39	$156.40	$156.40
Purchase #3	$77.88	13.232%	$88.1851	$88.19	$88.20	$88.20
Purchase #4	$86.85	13.591%	$98.6538	$98.65	$98.65	$98.70
Purchase #5	$130.71	10.846%	$144.8868	$144.89	$144.90	$144.90
Purchase #6	$84.82	4.380%	$88.5351	$88.54	$88.55	$88.50
Purchase #7	$116.91	12.706%	$131.7646	$131.76	$131.75	$131.80
7 purchase totals =	$884.76		$970.4198	$970.43	$970.45	$970.50