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 $40.82   13.161%   $46.1923   $46.19   $46.20   $46.20  
  Purchase #2 $138.61   12.532%   $155.9806   $155.98   $156.00   $156.00  
  Purchase #3 $241.50   13.269%   $273.5446   $273.54   $273.55   $273.50  
  Purchase #4 $246.99   7.871%   $266.4306   $266.43   $266.45   $266.40  
  Purchase #5 $103.40   10.184%   $113.9303   $113.93   $113.95   $113.90  
  Purchase #6 $234.62   11.419%   $261.4113   $261.41   $261.40   $261.40  
  Purchase #7 $51.37   13.222%   $58.1621   $58.16   $58.15   $58.20  
  7 purchase totals = $1,057.31       $1,175.6518   $1,175.64   $1,175.70   $1,175.60