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 $114.25   7.360%   $122.6588   $122.66   $122.65   $122.70  
  Purchase #2 $235.40   8.506%   $255.4231   $255.42   $255.40   $255.40  
  Purchase #3 $125.66   8.518%   $136.3637   $136.36   $136.35   $136.40  
  Purchase #4 $128.69   10.462%   $142.1535   $142.15   $142.15   $142.20  
  Purchase #5 $119.67   5.750%   $126.551   $126.55   $126.55   $126.60  
  Purchase #6 $166.26   10.169%   $183.167   $183.17   $183.15   $183.20  
  Purchase #7 $84.32   13.161%   $95.4174   $95.42   $95.40   $95.40  
  7 purchase totals = $974.25       $1,061.7345   $1,061.73   $1,061.65   $1,061.90