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	$235.82	8.323%	$255.4473	$255.45	$255.45	$255.40
Purchase #2	$92.49	5.418%	$97.5011	$97.50	$97.50	$97.50
Purchase #3	$107.97	4.139%	$112.4389	$112.44	$112.45	$112.40
Purchase #4	$131.66	7.827%	$141.965	$141.97	$141.95	$142.00
Purchase #5	$128.55	8.821%	$139.8894	$139.89	$139.90	$139.90
Purchase #6	$51.75	5.797%	$54.7499	$54.75	$54.75	$54.70
Purchase #7	$167.41	5.517%	$176.646	$176.65	$176.65	$176.60
7 purchase totals =	$915.65		$978.6376	$978.65	$978.65	$978.50