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	$35.54	12.810%	$40.0927	$40.09	$40.10	$40.10
Purchase #2	$142.59	10.778%	$157.9584	$157.96	$157.95	$158.00
Purchase #3	$134.99	13.790%	$153.6051	$153.61	$153.60	$153.60
Purchase #4	$165.48	10.273%	$182.4798	$182.48	$182.50	$182.50
Purchase #5	$205.81	7.334%	$220.9041	$220.90	$220.90	$220.90
Purchase #6	$134.35	6.309%	$142.8261	$142.83	$142.85	$142.80
Purchase #7	$169.32	9.309%	$185.082	$185.08	$185.10	$185.10
7 purchase totals =	$988.08		$1,082.9482	$1,082.95	$1,083.00	$1,083.00