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 $232.51   8.792%   $252.9523   $252.95   $252.95   $253.00  
  Purchase #2 $101.89   3.767%   $105.7282   $105.73   $105.75   $105.70  
  Purchase #3 $92.56   12.307%   $103.9514   $103.95   $103.95   $104.00  
  Purchase #4 $55.64   12.667%   $62.6879   $62.69   $62.70   $62.70  
  Purchase #5 $238.54   11.484%   $265.9339   $265.93   $265.95   $265.90  
  Purchase #6 $250.62   4.846%   $262.765   $262.77   $262.75   $262.80  
  Purchase #7 $227.98   8.367%   $247.0551   $247.06   $247.05   $247.10  
  7 purchase totals = $1,199.74       $1,301.0738   $1,301.08   $1,301.10   $1,301.20