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 $54.61   6.196%   $57.9936   $57.99   $58.00   $58.00  
  Purchase #2 $41.92   6.483%   $44.6377   $44.64   $44.65   $44.60  
  Purchase #3 $166.48   4.622%   $174.1747   $174.17   $174.15   $174.20  
  Purchase #4 $213.53   12.750%   $240.7551   $240.76   $240.75   $240.80  
  Purchase #5 $93.83   4.599%   $98.1452   $98.15   $98.15   $98.10  
  Purchase #6 $241.63   13.523%   $274.3056   $274.31   $274.30   $274.30  
  Purchase #7 $122.97   8.495%   $133.4163   $133.42   $133.40   $133.40  
  7 purchase totals = $934.97       $1,023.4282   $1,023.44   $1,023.40   $1,023.40