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 $52.25   13.341%   $59.2207   $59.22   $59.20   $59.20  
  Purchase #2 $112.48   13.418%   $127.5726   $127.57   $127.55   $127.60  
  Purchase #3 $77.70   3.817%   $80.6658   $80.67   $80.65   $80.70  
  Purchase #4 $30.30   12.412%   $34.0608   $34.06   $34.05   $34.10  
  Purchase #5 $222.36   6.436%   $236.6711   $236.67   $236.65   $236.70  
  Purchase #6 $244.88   11.469%   $272.9653   $272.97   $272.95   $273.00  
  Purchase #7 $76.85   10.202%   $84.6902   $84.69   $84.70   $84.70  
  7 purchase totals = $816.82       $895.8465   $895.85   $895.75   $896.00