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	$239.42	7.559%	$257.5178	$257.52	$257.50	$257.50
Purchase #2	$97.70	3.681%	$101.2963	$101.30	$101.30	$101.30
Purchase #3	$38.87	5.314%	$40.9356	$40.94	$40.95	$40.90
Purchase #4	$76.84	6.826%	$82.0851	$82.09	$82.10	$82.10
Purchase #5	$144.78	4.225%	$150.897	$150.90	$150.90	$150.90
Purchase #6	$171.90	13.379%	$194.8985	$194.90	$194.90	$194.90
Purchase #7	$109.49	5.330%	$115.3258	$115.33	$115.35	$115.30
7 purchase totals =	$879.00		$942.9561	$942.98	$943.00	$942.90