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	$152.83	6.827%	$163.2637	$163.26	$163.25	$163.30
Purchase #2	$132.95	3.391%	$137.4583	$137.46	$137.45	$137.50
Purchase #3	$214.89	11.165%	$238.8825	$238.88	$238.90	$238.90
Purchase #4	$51.89	12.222%	$58.232	$58.23	$58.25	$58.20
Purchase #5	$119.95	10.239%	$132.2317	$132.23	$132.25	$132.20
Purchase #6	$92.51	3.676%	$95.9107	$95.91	$95.90	$95.90
Purchase #7	$247.28	10.749%	$273.8601	$273.86	$273.85	$273.90
7 purchase totals =	$1,012.30		$1,099.8390	$1,099.83	$1,099.85	$1,099.90