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 $248.46   5.817%   $262.9129   $262.91   $262.90   $262.90  
  Purchase #2 $72.75   7.631%   $78.3016   $78.30   $78.30   $78.30  
  Purchase #3 $15.41   11.538%   $17.188   $17.19   $17.20   $17.20  
  Purchase #4 $193.51   7.295%   $207.6266   $207.63   $207.65   $207.60  
  Purchase #5 $161.45   11.126%   $179.4129   $179.41   $179.40   $179.40  
  Purchase #6 $62.59   13.231%   $70.8713   $70.87   $70.85   $70.90  
  Purchase #7 $222.76   9.403%   $243.7061   $243.71   $243.70   $243.70  
  7 purchase totals = $976.93       $1,060.0194   $1,060.02   $1,060.00   $1,060.00