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 $136.43   10.843%   $151.2231   $151.22   $151.20   $151.20  
  Purchase #2 $59.87   13.546%   $67.98   $67.98   $68.00   $68.00  
  Purchase #3 $76.67   3.375%   $79.2576   $79.26   $79.25   $79.30  
  Purchase #4 $130.46   5.745%   $137.9549   $137.95   $137.95   $138.00  
  Purchase #5 $110.45   3.569%   $114.392   $114.39   $114.40   $114.40  
  Purchase #6 $8.29   5.357%   $8.7341   $8.73   $8.75   $8.70  
  Purchase #7 $190.42   8.358%   $206.3353   $206.34   $206.35   $206.30  
  7 purchase totals = $712.59       $765.8770   $765.87   $765.90   $765.90