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 $161.95   8.274%   $175.3497   $175.35   $175.35   $175.30  
  Purchase #2 $131.95   7.577%   $141.9479   $141.95   $141.95   $141.90  
  Purchase #3 $217.59   3.438%   $225.0707   $225.07   $225.05   $225.10  
  Purchase #4 $119.87   6.527%   $127.6939   $127.69   $127.70   $127.70  
  Purchase #5 $153.32   4.592%   $160.3605   $160.36   $160.35   $160.40  
  Purchase #6 $234.36   11.723%   $261.834   $261.83   $261.85   $261.80  
  Purchase #7 $167.70   12.497%   $188.6575   $188.66   $188.65   $188.70  
  7 purchase totals = $1,186.74       $1,280.9142   $1,280.91   $1,280.90   $1,280.90