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 $206.95   9.190%   $225.9687   $225.97   $225.95   $226.00  
  Purchase #2 $85.58   12.226%   $96.043   $96.04   $96.05   $96.00  
  Purchase #3 $98.77   6.327%   $105.0192   $105.02   $105.00   $105.00  
  Purchase #4 $29.37   5.741%   $31.0561   $31.06   $31.05   $31.10  
  Purchase #5 $188.26   10.291%   $207.6338   $207.63   $207.65   $207.60  
  Purchase #6 $73.68   8.239%   $79.7505   $79.75   $79.75   $79.80  
  Purchase #7 $21.87   7.321%   $23.4711   $23.47   $23.45   $23.50  
  7 purchase totals = $704.48       $768.9424   $768.94   $768.90   $769.00