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 $240.30   10.269%   $264.9764   $264.98   $265.00   $265.00  
  Purchase #2 $234.68   11.594%   $261.8888   $261.89   $261.90   $261.90  
  Purchase #3 $17.59   13.872%   $20.0301   $20.03   $20.05   $20.00  
  Purchase #4 $82.57   12.634%   $93.0019   $93.00   $93.00   $93.00  
  Purchase #5 $14.88   6.647%   $15.8691   $15.87   $15.85   $15.90  
  Purchase #6 $113.76   6.717%   $121.4013   $121.40   $121.40   $121.40  
  Purchase #7 $148.42   3.391%   $153.4529   $153.45   $153.45   $153.50  
  7 purchase totals = $852.20       $930.6205   $930.62   $930.65   $930.70