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 $30.32   9.198%   $33.1088   $33.11   $33.10   $33.10  
  Purchase #2 $45.39   8.495%   $49.2459   $49.25   $49.25   $49.20  
  Purchase #3 $225.57   3.688%   $233.889   $233.89   $233.90   $233.90  
  Purchase #4 $27.58   10.163%   $30.383   $30.38   $30.40   $30.40  
  Purchase #5 $109.33   9.256%   $119.4496   $119.45   $119.45   $119.40  
  Purchase #6 $196.88   5.244%   $207.2044   $207.20   $207.20   $207.20  
  Purchase #7 $119.28   5.140%   $125.411   $125.41   $125.40   $125.40  
  7 purchase totals = $754.35       $798.6917   $798.69   $798.70   $798.60