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	$160.65	3.788%	$166.7354	$166.74	$166.75	$166.70
Purchase #2	$162.48	9.844%	$178.4745	$178.47	$178.45	$178.50
Purchase #3	$36.82	13.508%	$41.7936	$41.79	$41.80	$41.80
Purchase #4	$237.88	13.444%	$269.8606	$269.86	$269.85	$269.90
Purchase #5	$105.31	5.576%	$111.1821	$111.18	$111.20	$111.20
Purchase #6	$132.89	8.537%	$144.2348	$144.23	$144.25	$144.20
Purchase #7	$107.70	9.512%	$117.9444	$117.94	$117.95	$117.90
7 purchase totals =	$943.73		$1,030.2254	$1,030.21	$1,030.25	$1,030.20