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 $204.33   10.112%   $224.9918   $224.99   $225.00   $225.00  
  Purchase #2 $192.26   8.252%   $208.1253   $208.13   $208.15   $208.10  
  Purchase #3 $69.28   5.299%   $72.9511   $72.95   $72.95   $73.00  
  Purchase #4 $57.81   5.331%   $60.8919   $60.89   $60.90   $60.90  
  Purchase #5 $83.41   13.843%   $94.9564   $94.96   $94.95   $95.00  
  Purchase #6 $198.81   4.749%   $208.2515   $208.25   $208.25   $208.30  
  Purchase #7 $22.86   13.486%   $25.9429   $25.94   $25.95   $25.90  
  7 purchase totals = $828.76       $896.1109   $896.11   $896.15   $896.20