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 $184.81   5.414%   $194.8156   $194.82   $194.80   $194.80  
  Purchase #2 $184.93   3.795%   $191.9481   $191.95   $191.95   $191.90  
  Purchase #3 $69.75   13.638%   $79.2625   $79.26   $79.25   $79.30  
  Purchase #4 $133.29   4.790%   $139.6746   $139.67   $139.65   $139.70  
  Purchase #5 $222.76   5.462%   $234.9272   $234.93   $234.95   $234.90  
  Purchase #6 $108.29   4.537%   $113.2031   $113.20   $113.20   $113.20  
  Purchase #7 $10.41   6.202%   $11.0556   $11.06   $11.05   $11.10  
  7 purchase totals = $914.24       $964.8867   $964.89   $964.85   $964.90