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	$92.40	7.618%	$99.439	$99.44	$99.45	$99.40
Purchase #2	$142.65	9.311%	$155.9321	$155.93	$155.95	$155.90
Purchase #3	$124.78	13.579%	$141.7239	$141.72	$141.70	$141.70
Purchase #4	$237.55	8.429%	$257.5731	$257.57	$257.55	$257.60
Purchase #5	$79.94	12.560%	$89.9805	$89.98	$90.00	$90.00
Purchase #6	$85.41	6.506%	$90.9668	$90.97	$90.95	$91.00
Purchase #7	$139.86	10.720%	$154.853	$154.85	$154.85	$154.90
7 purchase totals =	$902.59		$990.4684	$990.46	$990.45	$990.50