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 $87.92   5.407%   $92.6738   $92.67   $92.65   $92.70  
  Purchase #2 $152.49   9.208%   $166.5313   $166.53   $166.55   $166.50  
  Purchase #3 $104.79   13.275%   $118.7009   $118.70   $118.70   $118.70  
  Purchase #4 $111.50   9.634%   $122.2419   $122.24   $122.25   $122.20  
  Purchase #5 $174.73   6.270%   $185.6856   $185.69   $185.70   $185.70  
  Purchase #6 $119.47   13.848%   $136.0142   $136.01   $136.00   $136.00  
  Purchase #7 $76.89   10.778%   $85.1772   $85.18   $85.20   $85.20  
  7 purchase totals = $827.79       $907.0249   $907.02   $907.05   $907.00