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 $94.32   12.579%   $106.1845   $106.18   $106.20   $106.20  
  Purchase #2 $22.69   8.416%   $24.5996   $24.60   $24.60   $24.60  
  Purchase #3 $57.80   5.126%   $60.7628   $60.76   $60.75   $60.80  
  Purchase #4 $38.92   10.204%   $42.8914   $42.89   $42.90   $42.90  
  Purchase #5 $109.39   7.393%   $117.4772   $117.48   $117.50   $117.50  
  Purchase #6 $243.44   7.811%   $262.4551   $262.46   $262.45   $262.50  
  Purchase #7 $224.53   13.836%   $255.596   $255.60   $255.60   $255.60  
  7 purchase totals = $791.09       $869.9666   $869.97   $870.00   $870.10