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	$38.27	8.161%	$41.3932	$41.39	$41.40	$41.40
Purchase #2	$122.55	12.539%	$137.9165	$137.92	$137.90	$137.90
Purchase #3	$240.54	10.742%	$266.3788	$266.38	$266.40	$266.40
Purchase #4	$95.83	7.424%	$102.9444	$102.94	$102.95	$102.90
Purchase #5	$137.53	9.481%	$150.5692	$150.57	$150.55	$150.60
Purchase #6	$126.75	11.617%	$141.4745	$141.47	$141.45	$141.50
Purchase #7	$250.92	12.537%	$282.3778	$282.38	$282.40	$282.40
7 purchase totals =	$1,012.39		$1,123.0544	$1,123.05	$1,123.05	$1,123.10