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 $117.94   13.848%   $134.2723   $134.27   $134.25   $134.30  
  Purchase #2 $125.95   12.225%   $141.3474   $141.35   $141.35   $141.30  
  Purchase #3 $107.29   6.678%   $114.4548   $114.45   $114.45   $114.50  
  Purchase #4 $75.89   12.646%   $85.487   $85.49   $85.50   $85.50  
  Purchase #5 $29.41   7.767%   $31.6943   $31.69   $31.70   $31.70  
  Purchase #6 $111.30   6.331%   $118.3464   $118.35   $118.35   $118.30  
  Purchase #7 $7.38   13.201%   $8.3542   $8.35   $8.35   $8.40  
  7 purchase totals = $575.16       $633.9564   $633.95   $633.95   $634.00