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 $45.81   8.557%   $49.73   $49.73   $49.75   $49.70  
  Purchase #2 $166.94   8.217%   $180.6575   $180.66   $180.65   $180.70  
  Purchase #3 $132.99   4.398%   $138.8389   $138.84   $138.85   $138.80  
  Purchase #4 $185.71   8.618%   $201.7145   $201.71   $201.70   $201.70  
  Purchase #5 $112.46   12.754%   $126.8031   $126.80   $126.80   $126.80  
  Purchase #6 $57.61   10.665%   $63.7541   $63.75   $63.75   $63.80  
  Purchase #7 $250.80   4.778%   $262.7832   $262.78   $262.80   $262.80  
  7 purchase totals = $952.32       $1,024.2813   $1,024.27   $1,024.30   $1,024.30