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 $237.68   3.738%   $246.5645   $246.56   $246.55   $246.60  
  Purchase #2 $113.30   8.188%   $122.577   $122.58   $122.60   $122.60  
  Purchase #3 $62.61   13.526%   $71.0786   $71.08   $71.10   $71.10  
  Purchase #4 $140.88   5.364%   $148.4368   $148.44   $148.45   $148.40  
  Purchase #5 $188.48   6.775%   $201.2495   $201.25   $201.25   $201.20  
  Purchase #6 $97.72   10.146%   $107.6347   $107.63   $107.65   $107.60  
  Purchase #7 $57.39   11.286%   $63.867   $63.87   $63.85   $63.90  
  7 purchase totals = $898.06       $961.4081   $961.41   $961.45   $961.40