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 $233.44   12.272%   $262.0878   $262.09   $262.10   $262.10  
  Purchase #2 $56.42   10.187%   $62.1675   $62.17   $62.15   $62.20  
  Purchase #3 $72.38   5.448%   $76.3233   $76.32   $76.30   $76.30  
  Purchase #4 $154.74   12.794%   $174.5374   $174.54   $174.55   $174.50  
  Purchase #5 $125.73   5.182%   $132.2453   $132.25   $132.25   $132.20  
  Purchase #6 $226.28   4.293%   $235.9942   $235.99   $236.00   $236.00  
  Purchase #7 $227.81   9.796%   $250.1263   $250.13   $250.15   $250.10  
  7 purchase totals = $1,096.80       $1,193.4818   $1,193.49   $1,193.50   $1,193.40