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 $223.62   10.739%   $247.6346   $247.63   $247.65   $247.60  
  Purchase #2 $94.53   4.574%   $98.8538   $98.85   $98.85   $98.90  
  Purchase #3 $241.35   8.216%   $261.1793   $261.18   $261.20   $261.20  
  Purchase #4 $15.46   10.260%   $17.0462   $17.05   $17.05   $17.00  
  Purchase #5 $71.40   9.310%   $78.0473   $78.05   $78.05   $78.00  
  Purchase #6 $106.62   9.857%   $117.1295   $117.13   $117.15   $117.10  
  Purchase #7 $87.88   4.151%   $91.5279   $91.53   $91.55   $91.50  
  7 purchase totals = $840.86       $911.4186   $911.42   $911.50   $911.30