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 $192.95   12.777%   $217.6032   $217.60   $217.60   $217.60  
  Purchase #2 $203.89   8.212%   $220.6334   $220.63   $220.65   $220.60  
  Purchase #3 $23.91   4.706%   $25.0352   $25.04   $25.05   $25.00  
  Purchase #4 $111.37   10.705%   $123.2922   $123.29   $123.30   $123.30  
  Purchase #5 $73.78   8.240%   $79.8595   $79.86   $79.85   $79.90  
  Purchase #6 $233.61   13.390%   $264.8904   $264.89   $264.90   $264.90  
  Purchase #7 $55.66   8.297%   $60.2781   $60.28   $60.30   $60.30  
  7 purchase totals = $895.17       $991.5920   $991.59   $991.65   $991.60