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 $201.88   10.681%   $223.4428   $223.44   $223.45   $223.40  
  Purchase #2 $95.41   9.534%   $104.5064   $104.51   $104.50   $104.50  
  Purchase #3 $112.44   9.315%   $122.9138   $122.91   $122.90   $122.90  
  Purchase #4 $58.78   10.448%   $64.9213   $64.92   $64.90   $64.90  
  Purchase #5 $125.31   7.659%   $134.9075   $134.91   $134.90   $134.90  
  Purchase #6 $34.97   7.252%   $37.506   $37.51   $37.50   $37.50  
  Purchase #7 $136.50   4.725%   $142.9496   $142.95   $142.95   $142.90  
  7 purchase totals = $765.29       $831.1474   $831.15   $831.10   $831.00