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	$39.86	4.844%	$41.7908	$41.79	$41.80	$41.80
Purchase #2	$116.61	6.439%	$124.1185	$124.12	$124.10	$124.10
Purchase #3	$235.45	4.703%	$246.5232	$246.52	$246.50	$246.50
Purchase #4	$145.25	5.280%	$152.9192	$152.92	$152.90	$152.90
Purchase #5	$69.79	4.382%	$72.8482	$72.85	$72.85	$72.80
Purchase #6	$125.72	5.724%	$132.9162	$132.92	$132.90	$132.90
Purchase #7	$213.75	13.562%	$242.7388	$242.74	$242.75	$242.70
7 purchase totals =	$946.43		$1,013.8549	$1,013.86	$1,013.80	$1,013.70