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 $60.95   8.311%   $66.0156   $66.02   $66.00   $66.00  
  Purchase #2 $219.47   8.286%   $237.6553   $237.66   $237.65   $237.70  
  Purchase #3 $32.32   7.426%   $34.7201   $34.72   $34.70   $34.70  
  Purchase #4 $76.48   12.321%   $85.9031   $85.90   $85.90   $85.90  
  Purchase #5 $157.36   4.596%   $164.5923   $164.59   $164.60   $164.60  
  Purchase #6 $42.73   12.815%   $48.2058   $48.21   $48.20   $48.20  
  Purchase #7 $227.68   6.409%   $242.272   $242.27   $242.25   $242.30  
  7 purchase totals = $816.99       $879.3642   $879.37   $879.30   $879.40