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 $207.83   11.123%   $230.9469   $230.95   $230.95   $230.90  
  Purchase #2 $40.58   13.322%   $45.9861   $45.99   $46.00   $46.00  
  Purchase #3 $201.46   10.433%   $222.4783   $222.48   $222.50   $222.50  
  Purchase #4 $229.90   13.265%   $260.3962   $260.40   $260.40   $260.40  
  Purchase #5 $110.36   8.348%   $119.5729   $119.57   $119.55   $119.60  
  Purchase #6 $170.48   11.188%   $189.5533   $189.55   $189.55   $189.60  
  Purchase #7 $173.74   11.480%   $193.6854   $193.69   $193.70   $193.70  
  7 purchase totals = $1,134.35       $1,262.6191   $1,262.63   $1,262.65   $1,262.70