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 $60.27   9.269%   $65.8564   $65.86   $65.85   $65.90  
  Purchase #2 $185.64   6.439%   $197.5934   $197.59   $197.60   $197.60  
  Purchase #3 $104.26   6.318%   $110.8471   $110.85   $110.85   $110.80  
  Purchase #4 $28.54   6.354%   $30.3534   $30.35   $30.35   $30.40  
  Purchase #5 $161.78   13.431%   $183.5087   $183.51   $183.50   $183.50  
  Purchase #6 $102.28   10.478%   $112.9969   $113.00   $113.00   $113.00  
  Purchase #7 $239.94   6.373%   $255.2314   $255.23   $255.25   $255.20  
  7 purchase totals = $882.71       $956.3873   $956.39   $956.40   $956.40