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 $236.85   8.814%   $257.726   $257.73   $257.75   $257.70  
  Purchase #2 $34.61   9.509%   $37.9011   $37.90   $37.90   $37.90  
  Purchase #3 $114.58   11.466%   $127.7177   $127.72   $127.70   $127.70  
  Purchase #4 $93.45   4.818%   $97.9524   $97.95   $97.95   $98.00  
  Purchase #5 $15.95   12.337%   $17.9178   $17.92   $17.90   $17.90  
  Purchase #6 $233.53   9.792%   $256.3973   $256.40   $256.40   $256.40  
  Purchase #7 $152.26   3.557%   $157.6759   $157.68   $157.70   $157.70  
  7 purchase totals = $881.23       $953.2882   $953.30   $953.30   $953.30