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	$78.98	9.784%	$86.7074	$86.71	$86.70	$86.70
Purchase #2	$53.91	10.334%	$59.4811	$59.48	$59.50	$59.50
Purchase #3	$138.64	8.704%	$150.7072	$150.71	$150.70	$150.70
Purchase #4	$200.84	6.315%	$213.523	$213.52	$213.50	$213.50
Purchase #5	$105.83	11.628%	$118.1359	$118.14	$118.15	$118.10
Purchase #6	$111.28	4.308%	$116.0739	$116.07	$116.05	$116.10
Purchase #7	$128.37	8.158%	$138.8424	$138.84	$138.85	$138.80
7 purchase totals =	$817.85		$883.4709	$883.47	$883.45	$883.40