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 $62.59   4.788%   $65.5868   $65.59   $65.60   $65.60  
  Purchase #2 $135.79   6.724%   $144.9205   $144.92   $144.90   $144.90  
  Purchase #3 $5.58   6.694%   $5.9535   $5.95   $5.95   $6.00  
  Purchase #4 $235.48   7.644%   $253.4801   $253.48   $253.50   $253.50  
  Purchase #5 $107.59   10.316%   $118.689   $118.69   $118.70   $118.70  
  Purchase #6 $117.34   4.681%   $122.8327   $122.83   $122.85   $122.80  
  Purchase #7 $28.84   5.252%   $30.3547   $30.35   $30.35   $30.40  
  7 purchase totals = $693.21       $741.8173   $741.81   $741.85   $741.90