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 $119.63   5.458%   $126.1594   $126.16   $126.15   $126.20  
  Purchase #2 $13.40   4.710%   $14.0311   $14.03   $14.05   $14.00  
  Purchase #3 $116.54   7.381%   $125.1418   $125.14   $125.15   $125.10  
  Purchase #4 $83.81   8.326%   $90.788   $90.79   $90.80   $90.80  
  Purchase #5 $76.27   6.454%   $81.1925   $81.19   $81.20   $81.20  
  Purchase #6 $225.55   3.301%   $232.9954   $233.00   $233.00   $233.00  
  Purchase #7 $104.83   13.268%   $118.7388   $118.74   $118.75   $118.70  
  7 purchase totals = $740.03       $789.0470   $789.05   $789.10   $789.00