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	$22.58	7.184%	$24.2021	$24.20	$24.20	$24.20
Purchase #2	$210.80	8.127%	$227.9317	$227.93	$227.95	$227.90
Purchase #3	$131.81	4.297%	$137.4739	$137.47	$137.45	$137.50
Purchase #4	$201.68	10.325%	$222.5035	$222.50	$222.50	$222.50
Purchase #5	$143.71	9.152%	$156.8623	$156.86	$156.85	$156.90
Purchase #6	$168.70	4.836%	$176.8583	$176.86	$176.85	$176.90
Purchase #7	$137.93	12.324%	$154.9285	$154.93	$154.95	$154.90
7 purchase totals =	$1,017.21		$1,100.7603	$1,100.75	$1,100.75	$1,100.80