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 $16.44   3.627%   $17.0363   $17.04   $17.05   $17.00  
  Purchase #2 $170.73   9.416%   $186.8059   $186.81   $186.80   $186.80  
  Purchase #3 $69.97   4.189%   $72.901   $72.90   $72.90   $72.90  
  Purchase #4 $39.32   11.175%   $43.714   $43.71   $43.70   $43.70  
  Purchase #5 $246.75   12.114%   $276.6413   $276.64   $276.65   $276.60  
  Purchase #6 $163.72   11.423%   $182.4217   $182.42   $182.40   $182.40  
  Purchase #7 $59.33   5.462%   $62.5706   $62.57   $62.55   $62.60  
  7 purchase totals = $766.26       $842.0908   $842.09   $842.05   $842.00