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 $228.81   13.522%   $259.7497   $259.75   $259.75   $259.70  
  Purchase #2 $93.83   4.628%   $98.1725   $98.17   $98.15   $98.20  
  Purchase #3 $158.38   8.261%   $171.4638   $171.46   $171.45   $171.50  
  Purchase #4 $181.52   8.176%   $196.3611   $196.36   $196.35   $196.40  
  Purchase #5 $168.85   9.777%   $185.3585   $185.36   $185.35   $185.40  
  Purchase #6 $241.96   6.517%   $257.7285   $257.73   $257.75   $257.70  
  Purchase #7 $119.60   12.491%   $134.5392   $134.54   $134.55   $134.50  
  7 purchase totals = $1,192.95       $1,303.3733   $1,303.37   $1,303.35   $1,303.40