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	$242.30	6.291%	$257.5431	$257.54	$257.55	$257.50
Purchase #2	$102.83	9.334%	$112.4282	$112.43	$112.45	$112.40
Purchase #3	$198.27	8.742%	$215.6028	$215.60	$215.60	$215.60
Purchase #4	$14.44	8.592%	$15.6807	$15.68	$15.70	$15.70
Purchase #5	$72.90	10.113%	$80.2724	$80.27	$80.25	$80.30
Purchase #6	$179.48	11.814%	$200.6838	$200.68	$200.70	$200.70
Purchase #7	$52.71	12.629%	$59.3667	$59.37	$59.35	$59.40
7 purchase totals =	$862.93		$941.5777	$941.57	$941.60	$941.60