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	$123.31	6.611%	$131.462	$131.46	$131.45	$131.50
Purchase #2	$82.75	4.246%	$86.2636	$86.26	$86.25	$86.30
Purchase #3	$158.88	4.534%	$166.0836	$166.08	$166.10	$166.10
Purchase #4	$219.83	8.651%	$238.8475	$238.85	$238.85	$238.80
Purchase #5	$61.53	9.627%	$67.4535	$67.45	$67.45	$67.50
Purchase #6	$97.25	7.662%	$104.7013	$104.70	$104.70	$104.70
Purchase #7	$143.50	12.505%	$161.4447	$161.44	$161.45	$161.40
7 purchase totals =	$887.05		$956.2562	$956.24	$956.25	$956.30