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 $24.65   6.203%   $26.179   $26.18   $26.20   $26.20  
  Purchase #2 $237.39   8.835%   $258.3634   $258.36   $258.35   $258.40  
  Purchase #3 $250.35   3.258%   $258.5064   $258.51   $258.50   $258.50  
  Purchase #4 $26.56   4.605%   $27.7831   $27.78   $27.80   $27.80  
  Purchase #5 $155.57   11.356%   $173.2365   $173.24   $173.25   $173.20  
  Purchase #6 $100.28   5.683%   $105.9789   $105.98   $106.00   $106.00  
  Purchase #7 $161.39   4.616%   $168.8398   $168.84   $168.85   $168.80  
  7 purchase totals = $956.19       $1,018.8871   $1,018.89   $1,018.95   $1,018.90