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 $238.54   7.439%   $256.285   $256.29   $256.30   $256.30  
  Purchase #2 $126.84   11.507%   $141.4355   $141.44   $141.45   $141.40  
  Purchase #3 $101.44   13.289%   $114.9204   $114.92   $114.90   $114.90  
  Purchase #4 $164.78   3.135%   $169.9459   $169.95   $169.95   $169.90  
  Purchase #5 $215.75   5.443%   $227.4933   $227.49   $227.50   $227.50  
  Purchase #6 $141.94   3.421%   $146.7958   $146.80   $146.80   $146.80  
  Purchase #7 $191.89   7.176%   $205.66   $205.66   $205.65   $205.70  
  7 purchase totals = $1,181.18       $1,262.5359   $1,262.55   $1,262.55   $1,262.50