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 $119.35   12.116%   $133.8104   $133.81   $133.80   $133.80  
  Purchase #2 $179.53   9.579%   $196.7272   $196.73   $196.75   $196.70  
  Purchase #3 $121.90   9.805%   $133.8523   $133.85   $133.85   $133.90  
  Purchase #4 $190.78   3.425%   $197.3142   $197.31   $197.30   $197.30  
  Purchase #5 $48.46   3.586%   $50.1978   $50.20   $50.20   $50.20  
  Purchase #6 $57.84   11.797%   $64.6634   $64.66   $64.65   $64.70  
  Purchase #7 $248.25   8.639%   $269.6963   $269.70   $269.70   $269.70  
  7 purchase totals = $966.11       $1,046.2616   $1,046.26   $1,046.25   $1,046.30