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 $58.48   5.348%   $61.6075   $61.61   $61.60   $61.60  
  Purchase #2 $85.63   13.638%   $97.3082   $97.31   $97.30   $97.30  
  Purchase #3 $239.83   13.421%   $272.0176   $272.02   $272.00   $272.00  
  Purchase #4 $134.26   8.870%   $146.1689   $146.17   $146.15   $146.20  
  Purchase #5 $232.30   10.626%   $256.9842   $256.98   $257.00   $257.00  
  Purchase #6 $200.84   13.588%   $228.1301   $228.13   $228.15   $228.10  
  Purchase #7 $188.48   10.482%   $208.2365   $208.24   $208.25   $208.20  
  7 purchase totals = $1,139.82       $1,270.4530   $1,270.46   $1,270.45   $1,270.40