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 $164.97   10.262%   $181.8992   $181.90   $181.90   $181.90  
  Purchase #2 $221.61   12.814%   $250.0071   $250.01   $250.00   $250.00  
  Purchase #3 $39.87   9.528%   $43.6688   $43.67   $43.65   $43.70  
  Purchase #4 $104.71   9.779%   $114.9496   $114.95   $114.95   $114.90  
  Purchase #5 $117.41   13.675%   $133.4658   $133.47   $133.45   $133.50  
  Purchase #6 $14.46   7.204%   $15.5017   $15.50   $15.50   $15.50  
  Purchase #7 $242.58   12.841%   $273.7297   $273.73   $273.75   $273.70  
  7 purchase totals = $905.61       $1,013.2219   $1,013.23   $1,013.20   $1,013.20