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 $48.57   10.610%   $53.7233   $53.72   $53.70   $53.70  
  Purchase #2 $231.69   6.868%   $247.6025   $247.60   $247.60   $247.60  
  Purchase #3 $146.78   12.195%   $164.6798   $164.68   $164.70   $164.70  
  Purchase #4 $9.95   9.642%   $10.9094   $10.91   $10.90   $10.90  
  Purchase #5 $23.49   4.744%   $24.6044   $24.60   $24.60   $24.60  
  Purchase #6 $249.63   8.193%   $270.0822   $270.08   $270.10   $270.10  
  Purchase #7 $69.51   4.829%   $72.8666   $72.87   $72.85   $72.90  
  7 purchase totals = $779.62       $844.4682   $844.46   $844.45   $844.50