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 $84.61   13.254%   $95.8242   $95.82   $95.80   $95.80  
  Purchase #2 $76.42   8.446%   $82.8744   $82.87   $82.85   $82.90  
  Purchase #3 $224.49   10.653%   $248.4049   $248.40   $248.40   $248.40  
  Purchase #4 $198.61   12.106%   $222.6537   $222.65   $222.65   $222.70  
  Purchase #5 $55.55   12.352%   $62.4115   $62.41   $62.40   $62.40  
  Purchase #6 $125.50   10.625%   $138.8344   $138.83   $138.85   $138.80  
  Purchase #7 $117.61   7.734%   $126.706   $126.71   $126.70   $126.70  
  7 purchase totals = $882.79       $977.7091   $977.69   $977.65   $977.70