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 $51.86   8.150%   $56.0866   $56.09   $56.10   $56.10  
  Purchase #2 $84.32   12.252%   $94.6509   $94.65   $94.65   $94.70  
  Purchase #3 $33.94   9.611%   $37.202   $37.20   $37.20   $37.20  
  Purchase #4 $182.77   11.726%   $204.2016   $204.20   $204.20   $204.20  
  Purchase #5 $124.43   8.604%   $135.136   $135.14   $135.15   $135.10  
  Purchase #6 $59.77   8.131%   $64.6299   $64.63   $64.65   $64.60  
  Purchase #7 $188.60   10.579%   $208.552   $208.55   $208.55   $208.60  
  7 purchase totals = $725.69       $800.4590   $800.46   $800.50   $800.50