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 $246.83   9.206%   $269.5532   $269.55   $269.55   $269.60  
  Purchase #2 $97.83   9.374%   $107.0006   $107.00   $107.00   $107.00  
  Purchase #3 $28.28   8.808%   $30.7709   $30.77   $30.75   $30.80  
  Purchase #4 $147.56   8.473%   $160.0628   $160.06   $160.05   $160.10  
  Purchase #5 $183.71   6.694%   $196.0075   $196.01   $196.00   $196.00  
  Purchase #6 $182.36   3.584%   $188.8958   $188.90   $188.90   $188.90  
  Purchase #7 $58.72   5.112%   $61.7218   $61.72   $61.70   $61.70  
  7 purchase totals = $945.29       $1,014.0126   $1,014.01   $1,013.95   $1,014.10