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 $204.69   13.795%   $232.927   $232.93   $232.95   $232.90  
  Purchase #2 $233.63   7.239%   $250.5425   $250.54   $250.55   $250.50  
  Purchase #3 $135.73   11.368%   $151.1598   $151.16   $151.15   $151.20  
  Purchase #4 $66.71   10.808%   $73.92   $73.92   $73.90   $73.90  
  Purchase #5 $150.97   4.172%   $157.2685   $157.27   $157.25   $157.30  
  Purchase #6 $128.83   8.476%   $139.7496   $139.75   $139.75   $139.70  
  Purchase #7 $233.36   10.322%   $257.4474   $257.45   $257.45   $257.40  
  7 purchase totals = $1,153.92       $1,263.0148   $1,263.02   $1,263.00   $1,262.90