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 $49.84   13.623%   $56.6297   $56.63   $56.65   $56.60  
  Purchase #2 $112.38   5.209%   $118.2339   $118.23   $118.25   $118.20  
  Purchase #3 $54.32   7.474%   $58.3799   $58.38   $58.40   $58.40  
  Purchase #4 $177.32   7.665%   $190.9116   $190.91   $190.90   $190.90  
  Purchase #5 $247.79   7.284%   $265.839   $265.84   $265.85   $265.80  
  Purchase #6 $12.36   10.808%   $13.6959   $13.70   $13.70   $13.70  
  Purchase #7 $216.86   13.155%   $245.3879   $245.39   $245.40   $245.40  
  7 purchase totals = $870.87       $949.0779   $949.08   $949.15   $949.00