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 $31.35   8.859%   $34.1273   $34.13   $34.15   $34.10  
  Purchase #2 $218.53   7.831%   $235.6431   $235.64   $235.65   $235.60  
  Purchase #3 $162.38   8.538%   $176.244   $176.24   $176.25   $176.20  
  Purchase #4 $104.41   4.170%   $108.7639   $108.76   $108.75   $108.80  
  Purchase #5 $250.38   3.699%   $259.6416   $259.64   $259.65   $259.60  
  Purchase #6 $41.37   4.558%   $43.2556   $43.26   $43.25   $43.30  
  Purchase #7 $77.39   7.291%   $83.0325   $83.03   $83.05   $83.00  
  7 purchase totals = $885.81       $940.7080   $940.70   $940.75   $940.60