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	$115.84	13.419%	$131.3846	$131.38	$131.40	$131.40
Purchase #2	$222.58	6.252%	$236.4957	$236.50	$236.50	$236.50
Purchase #3	$126.73	10.780%	$140.3915	$140.39	$140.40	$140.40
Purchase #4	$118.59	3.429%	$122.6565	$122.66	$122.65	$122.70
Purchase #5	$85.57	4.115%	$89.0912	$89.09	$89.10	$89.10
Purchase #6	$134.74	7.509%	$144.8576	$144.86	$144.85	$144.90
Purchase #7	$70.98	13.740%	$80.7327	$80.73	$80.75	$80.70
7 purchase totals =	$875.03		$945.6098	$945.61	$945.65	$945.70