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	$73.75	13.278%	$83.5425	$83.54	$83.55	$83.50
Purchase #2	$226.89	13.509%	$257.5406	$257.54	$257.55	$257.50
Purchase #3	$63.72	5.597%	$67.2864	$67.29	$67.30	$67.30
Purchase #4	$58.63	5.462%	$61.8324	$61.83	$61.85	$61.80
Purchase #5	$62.50	10.202%	$68.8763	$68.88	$68.90	$68.90
Purchase #6	$149.39	6.317%	$158.827	$158.83	$158.85	$158.80
Purchase #7	$160.89	4.189%	$167.6297	$167.63	$167.65	$167.60
7 purchase totals =	$795.77		$865.5349	$865.54	$865.65	$865.40