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 $245.50   6.194%   $260.7063   $260.71   $260.70   $260.70  
  Purchase #2 $228.48   10.541%   $252.5641   $252.56   $252.55   $252.60  
  Purchase #3 $98.99   12.307%   $111.1727   $111.17   $111.15   $111.20  
  Purchase #4 $17.95   6.556%   $19.1268   $19.13   $19.15   $19.10  
  Purchase #5 $206.45   9.727%   $226.5314   $226.53   $226.55   $226.50  
  Purchase #6 $18.42   13.744%   $20.9516   $20.95   $20.95   $21.00  
  Purchase #7 $41.97   3.484%   $43.4322   $43.43   $43.45   $43.40  
  7 purchase totals = $857.76       $934.4851   $934.48   $934.50   $934.50