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 $124.73   11.845%   $139.5043   $139.50   $139.50   $139.50  
  Purchase #2 $112.51   8.829%   $122.4435   $122.44   $122.45   $122.40  
  Purchase #3 $45.86   11.586%   $51.1733   $51.17   $51.15   $51.20  
  Purchase #4 $45.25   9.475%   $49.5374   $49.54   $49.55   $49.50  
  Purchase #5 $220.65   13.181%   $249.7339   $249.73   $249.75   $249.70  
  Purchase #6 $121.42   8.387%   $131.6035   $131.60   $131.60   $131.60  
  Purchase #7 $240.41   12.633%   $270.781   $270.78   $270.80   $270.80  
  7 purchase totals = $910.83       $1,014.7769   $1,014.76   $1,014.80   $1,014.70