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 $184.84   4.874%   $193.8491   $193.85   $193.85   $193.80  
  Purchase #2 $69.86   5.509%   $73.7086   $73.71   $73.70   $73.70  
  Purchase #3 $16.69   7.202%   $17.892   $17.89   $17.90   $17.90  
  Purchase #4 $171.93   9.835%   $188.8393   $188.84   $188.85   $188.80  
  Purchase #5 $241.93   3.287%   $249.8822   $249.88   $249.90   $249.90  
  Purchase #6 $20.29   11.587%   $22.641   $22.64   $22.65   $22.60  
  Purchase #7 $174.92   4.527%   $182.8386   $182.84   $182.85   $182.80  
  7 purchase totals = $880.46       $929.6508   $929.65   $929.70   $929.50