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 $50.96   13.796%   $57.9904   $57.99   $58.00   $58.00  
  Purchase #2 $242.94   13.626%   $276.043   $276.04   $276.05   $276.00  
  Purchase #3 $99.43   13.573%   $112.9256   $112.93   $112.95   $112.90  
  Purchase #4 $194.42   12.274%   $218.2831   $218.28   $218.30   $218.30  
  Purchase #5 $248.29   5.289%   $261.4221   $261.42   $261.40   $261.40  
  Purchase #6 $236.65   10.358%   $261.1622   $261.16   $261.15   $261.20  
  Purchase #7 $73.91   10.651%   $81.7822   $81.78   $81.80   $81.80  
  7 purchase totals = $1,146.60       $1,269.6086   $1,269.60   $1,269.65   $1,269.60