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 $249.93   10.534%   $276.2576   $276.26   $276.25   $276.30  
  Purchase #2 $184.35   6.294%   $195.953   $195.95   $195.95   $196.00  
  Purchase #3 $101.89   8.612%   $110.6648   $110.66   $110.65   $110.70  
  Purchase #4 $126.29   10.377%   $139.3951   $139.40   $139.40   $139.40  
  Purchase #5 $242.92   5.172%   $255.4838   $255.48   $255.50   $255.50  
  Purchase #6 $134.32   8.769%   $146.0985   $146.10   $146.10   $146.10  
  Purchase #7 $125.89   8.202%   $136.2155   $136.22   $136.20   $136.20  
  7 purchase totals = $1,165.59       $1,260.0683   $1,260.07   $1,260.05   $1,260.20