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 $60.78   4.556%   $63.5491   $63.55   $63.55   $63.50  
  Purchase #2 $152.39   4.773%   $159.6636   $159.66   $159.65   $159.70  
  Purchase #3 $77.75   10.704%   $86.0724   $86.07   $86.05   $86.10  
  Purchase #4 $83.95   10.652%   $92.8924   $92.89   $92.90   $92.90  
  Purchase #5 $154.49   13.484%   $175.3214   $175.32   $175.30   $175.30  
  Purchase #6 $149.69   5.611%   $158.0891   $158.09   $158.10   $158.10  
  Purchase #7 $28.86   11.828%   $32.2736   $32.27   $32.25   $32.30  
  7 purchase totals = $707.91       $767.8616   $767.85   $767.80   $767.90