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 $186.46   8.153%   $201.6621   $201.66   $201.65   $201.70  
  Purchase #2 $34.89   4.406%   $36.4273   $36.43   $36.45   $36.40  
  Purchase #3 $181.93   8.317%   $197.0611   $197.06   $197.05   $197.10  
  Purchase #4 $182.61   4.568%   $190.9516   $190.95   $190.95   $191.00  
  Purchase #5 $208.61   13.577%   $236.933   $236.93   $236.95   $236.90  
  Purchase #6 $77.93   9.705%   $85.4931   $85.49   $85.50   $85.50  
  Purchase #7 $118.44   4.178%   $123.3884   $123.39   $123.40   $123.40  
  7 purchase totals = $990.87       $1,071.9166   $1,071.91   $1,071.95   $1,072.00