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 $233.44   12.520%   $262.6667   $262.67   $262.65   $262.70  
  Purchase #2 $38.33   3.528%   $39.6823   $39.68   $39.70   $39.70  
  Purchase #3 $55.85   11.516%   $62.2817   $62.28   $62.30   $62.30  
  Purchase #4 $125.77   9.563%   $137.7974   $137.80   $137.80   $137.80  
  Purchase #5 $69.30   10.210%   $76.3755   $76.38   $76.40   $76.40  
  Purchase #6 $76.67   6.665%   $81.7801   $81.78   $81.80   $81.80  
  Purchase #7 $137.45   12.124%   $154.1144   $154.11   $154.10   $154.10  
  7 purchase totals = $736.81       $814.6981   $814.70   $814.75   $814.80