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 $47.25   3.791%   $49.0412   $49.04   $49.05   $49.00  
  Purchase #2 $59.86   13.284%   $67.8118   $67.81   $67.80   $67.80  
  Purchase #3 $205.36   10.729%   $227.3931   $227.39   $227.40   $227.40  
  Purchase #4 $63.86   9.129%   $69.6898   $69.69   $69.70   $69.70  
  Purchase #5 $227.41   8.782%   $247.3811   $247.38   $247.40   $247.40  
  Purchase #6 $179.91   10.357%   $198.5433   $198.54   $198.55   $198.50  
  Purchase #7 $77.71   8.874%   $84.606   $84.61   $84.60   $84.60  
  7 purchase totals = $861.36       $944.4663   $944.46   $944.50   $944.40