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 $111.70   6.725%   $119.2118   $119.21   $119.20   $119.20  
  Purchase #2 $209.53   7.212%   $224.6413   $224.64   $224.65   $224.60  
  Purchase #3 $53.83   6.416%   $57.2837   $57.28   $57.30   $57.30  
  Purchase #4 $207.86   12.664%   $234.1834   $234.18   $234.20   $234.20  
  Purchase #5 $79.63   13.613%   $90.47   $90.47   $90.45   $90.50  
  Purchase #6 $14.31   10.475%   $15.809   $15.81   $15.80   $15.80  
  Purchase #7 $249.33   8.850%   $271.3957   $271.40   $271.40   $271.40  
  7 purchase totals = $926.19       $1,012.9949   $1,012.99   $1,013.00   $1,013.00