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 $232.79   5.646%   $245.9333   $245.93   $245.95   $245.90  
  Purchase #2 $75.40   8.358%   $81.7019   $81.70   $81.70   $81.70  
  Purchase #3 $240.99   8.471%   $261.4043   $261.40   $261.40   $261.40  
  Purchase #4 $229.78   8.213%   $248.6518   $248.65   $248.65   $248.70  
  Purchase #5 $58.27   11.583%   $65.0194   $65.02   $65.00   $65.00  
  Purchase #6 $71.89   13.866%   $81.8583   $81.86   $81.85   $81.90  
  Purchase #7 $119.46   4.761%   $125.1475   $125.15   $125.15   $125.10  
  7 purchase totals = $1,028.58       $1,109.7165   $1,109.71   $1,109.70   $1,109.70