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 $209.93   12.596%   $236.3728   $236.37   $236.35   $236.40  
  Purchase #2 $119.74   5.853%   $126.7484   $126.75   $126.75   $126.70  
  Purchase #3 $59.71   13.873%   $67.9936   $67.99   $68.00   $68.00  
  Purchase #4 $200.35   8.757%   $217.8946   $217.89   $217.90   $217.90  
  Purchase #5 $63.57   8.361%   $68.8851   $68.89   $68.90   $68.90  
  Purchase #6 $166.64   5.853%   $176.3934   $176.39   $176.40   $176.40  
  Purchase #7 $104.85   12.216%   $117.6585   $117.66   $117.65   $117.70  
  7 purchase totals = $924.79       $1,011.9464   $1,011.94   $1,011.95   $1,012.00