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 $65.31   8.179%   $70.6517   $70.65   $70.65   $70.70  
  Purchase #2 $206.51   3.641%   $214.029   $214.03   $214.05   $214.00  
  Purchase #3 $195.63   6.576%   $208.4946   $208.49   $208.50   $208.50  
  Purchase #4 $110.47   7.697%   $118.9729   $118.97   $118.95   $119.00  
  Purchase #5 $115.95   13.421%   $131.5116   $131.51   $131.50   $131.50  
  Purchase #6 $57.79   6.594%   $61.6007   $61.60   $61.60   $61.60  
  Purchase #7 $10.34   8.217%   $11.1896   $11.19   $11.20   $11.20  
  7 purchase totals = $762.00       $816.4501   $816.44   $816.45   $816.50