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 $48.71   8.654%   $52.9254   $52.93   $52.95   $52.90  
  Purchase #2 $63.25   8.383%   $68.5522   $68.55   $68.55   $68.60  
  Purchase #3 $151.27   10.344%   $166.9174   $166.92   $166.90   $166.90  
  Purchase #4 $240.81   10.231%   $265.4473   $265.45   $265.45   $265.40  
  Purchase #5 $225.39   12.533%   $253.6381   $253.64   $253.65   $253.60  
  Purchase #6 $164.39   4.555%   $171.878   $171.88   $171.90   $171.90  
  Purchase #7 $26.94   13.763%   $30.6478   $30.65   $30.65   $30.60  
  7 purchase totals = $920.76       $1,010.0062   $1,010.02   $1,010.05   $1,009.90