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 $21.69   5.555%   $22.8949   $22.89   $22.90   $22.90  
  Purchase #2 $192.56   10.234%   $212.2666   $212.27   $212.25   $212.30  
  Purchase #3 $177.31   6.458%   $188.7607   $188.76   $188.75   $188.80  
  Purchase #4 $184.71   3.746%   $191.6292   $191.63   $191.65   $191.60  
  Purchase #5 $66.99   4.299%   $69.8699   $69.87   $69.85   $69.90  
  Purchase #6 $196.99   11.769%   $220.1738   $220.17   $220.15   $220.20  
  Purchase #7 $48.74   3.652%   $50.52   $50.52   $50.50   $50.50  
  7 purchase totals = $888.99       $956.1151   $956.11   $956.05   $956.20