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	$205.39	12.738%	$231.5526	$231.55	$231.55	$231.60
Purchase #2	$37.46	7.751%	$40.3635	$40.36	$40.35	$40.40
Purchase #3	$112.66	10.445%	$124.4273	$124.43	$124.45	$124.40
Purchase #4	$54.70	11.517%	$60.9998	$61.00	$61.00	$61.00
Purchase #5	$78.83	13.738%	$89.6597	$89.66	$89.65	$89.70
Purchase #6	$249.49	3.148%	$257.3439	$257.34	$257.35	$257.30
Purchase #7	$128.57	10.835%	$142.5006	$142.50	$142.50	$142.50
7 purchase totals =	$867.10		$946.8474	$946.84	$946.85	$946.90