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 $53.87   10.531%   $59.543   $59.54   $59.55   $59.50  
  Purchase #2 $76.34   13.451%   $86.6085   $86.61   $86.60   $86.60  
  Purchase #3 $44.64   13.831%   $50.8142   $50.81   $50.80   $50.80  
  Purchase #4 $112.97   10.865%   $125.2442   $125.24   $125.25   $125.20  
  Purchase #5 $104.78   13.639%   $119.0709   $119.07   $119.05   $119.10  
  Purchase #6 $240.50   4.845%   $252.1522   $252.15   $252.15   $252.20  
  Purchase #7 $230.35   13.158%   $260.6595   $260.66   $260.65   $260.70  
  7 purchase totals = $863.45       $954.0925   $954.08   $954.05   $954.10