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	$161.94	12.155%	$181.6238	$181.62	$181.60	$181.60
Purchase #2	$142.59	8.330%	$154.4677	$154.47	$154.45	$154.50
Purchase #3	$225.46	6.864%	$240.9356	$240.94	$240.95	$240.90
Purchase #4	$139.56	8.541%	$151.4798	$151.48	$151.50	$151.50
Purchase #5	$84.89	5.388%	$89.4639	$89.46	$89.45	$89.50
Purchase #6	$248.70	11.693%	$277.7805	$277.78	$277.80	$277.80
Purchase #7	$117.79	12.152%	$132.1038	$132.10	$132.10	$132.10
7 purchase totals =	$1,120.93		$1,227.8551	$1,227.85	$1,227.85	$1,227.90