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 $52.82   7.326%   $56.6896   $56.69   $56.70   $56.70  
  Purchase #2 $134.71   8.382%   $146.0014   $146.00   $146.00   $146.00  
  Purchase #3 $245.89   10.724%   $272.2592   $272.26   $272.25   $272.30  
  Purchase #4 $121.53   11.249%   $135.2009   $135.20   $135.20   $135.20  
  Purchase #5 $59.47   7.411%   $63.8773   $63.88   $63.90   $63.90  
  Purchase #6 $207.40   10.717%   $229.6271   $229.63   $229.65   $229.60  
  Purchase #7 $193.41   5.539%   $204.123   $204.12   $204.10   $204.10  
  7 purchase totals = $1,015.23       $1,107.7785   $1,107.78   $1,107.80   $1,107.80