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	$180.82	5.550%	$190.8555	$190.86	$190.85	$190.90
Purchase #2	$164.54	6.195%	$174.7333	$174.73	$174.75	$174.70
Purchase #3	$97.90	9.300%	$107.0047	$107.00	$107.00	$107.00
Purchase #4	$78.93	5.280%	$83.0975	$83.10	$83.10	$83.10
Purchase #5	$123.82	8.119%	$133.8729	$133.87	$133.85	$133.90
Purchase #6	$52.63	12.296%	$59.1014	$59.10	$59.10	$59.10
Purchase #7	$20.82	8.554%	$22.6009	$22.60	$22.60	$22.60
7 purchase totals =	$719.46		$771.2662	$771.26	$771.25	$771.30