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 $247.66   13.836%   $281.9262   $281.93   $281.95   $281.90  
  Purchase #2 $209.70   12.163%   $235.2058   $235.21   $235.20   $235.20  
  Purchase #3 $51.81   13.514%   $58.8116   $58.81   $58.80   $58.80  
  Purchase #4 $197.72   5.280%   $208.1596   $208.16   $208.15   $208.20  
  Purchase #5 $186.35   6.464%   $198.3957   $198.40   $198.40   $198.40  
  Purchase #6 $186.36   6.714%   $198.8722   $198.87   $198.85   $198.90  
  Purchase #7 $168.45   4.430%   $175.9123   $175.91   $175.90   $175.90  
  7 purchase totals = $1,248.05       $1,357.2834   $1,357.29   $1,357.25   $1,357.30