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	$104.59	4.698%	$109.5036	$109.50	$109.50	$109.50
Purchase #2	$69.89	4.748%	$73.2084	$73.21	$73.20	$73.20
Purchase #3	$231.27	10.446%	$255.4285	$255.43	$255.45	$255.40
Purchase #4	$119.38	11.795%	$133.4609	$133.46	$133.45	$133.50
Purchase #5	$189.28	13.559%	$214.9445	$214.94	$214.95	$214.90
Purchase #6	$41.97	10.833%	$46.5166	$46.52	$46.50	$46.50
Purchase #7	$236.94	12.162%	$265.7566	$265.76	$265.75	$265.80
7 purchase totals =	$993.32		$1,098.8191	$1,098.82	$1,098.80	$1,098.80