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 $191.86   7.693%   $206.6198   $206.62   $206.60   $206.60  
  Purchase #2 $64.84   7.521%   $69.7166   $69.72   $69.70   $69.70  
  Purchase #3 $9.89   4.183%   $10.3037   $10.30   $10.30   $10.30  
  Purchase #4 $119.30   12.546%   $134.2674   $134.27   $134.25   $134.30  
  Purchase #5 $187.97   6.557%   $200.2952   $200.30   $200.30   $200.30  
  Purchase #6 $188.76   10.314%   $208.2287   $208.23   $208.25   $208.20  
  Purchase #7 $126.51   10.462%   $139.7455   $139.75   $139.75   $139.70  
  7 purchase totals = $889.13       $969.1769   $969.19   $969.15   $969.10