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 $66.29   8.169%   $71.7052   $71.71   $71.70   $71.70  
  Purchase #2 $215.92   10.473%   $238.5333   $238.53   $238.55   $238.50  
  Purchase #3 $245.69   5.203%   $258.4733   $258.47   $258.45   $258.50  
  Purchase #4 $231.36   8.272%   $250.4981   $250.50   $250.50   $250.50  
  Purchase #5 $59.76   11.540%   $66.6563   $66.66   $66.65   $66.70  
  Purchase #6 $84.57   11.334%   $94.1552   $94.16   $94.15   $94.20  
  Purchase #7 $163.79   9.358%   $179.1175   $179.12   $179.10   $179.10  
  7 purchase totals = $1,067.38       $1,159.1389   $1,159.15   $1,159.10   $1,159.20