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 $55.48   12.806%   $62.5848   $62.58   $62.60   $62.60  
  Purchase #2 $232.75   10.571%   $257.354   $257.35   $257.35   $257.40  
  Purchase #3 $133.45   4.760%   $139.8022   $139.80   $139.80   $139.80  
  Purchase #4 $10.96   6.644%   $11.6882   $11.69   $11.70   $11.70  
  Purchase #5 $186.61   3.563%   $193.2589   $193.26   $193.25   $193.30  
  Purchase #6 $198.58   8.650%   $215.7572   $215.76   $215.75   $215.80  
  Purchase #7 $50.82   5.598%   $53.6649   $53.66   $53.65   $53.70  
  7 purchase totals = $868.65       $934.1102   $934.10   $934.10   $934.30