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 $88.89   8.771%   $96.6865   $96.69   $96.70   $96.70  
  Purchase #2 $27.60   10.381%   $30.4652   $30.47   $30.45   $30.50  
  Purchase #3 $23.53   8.842%   $25.6105   $25.61   $25.60   $25.60  
  Purchase #4 $19.70   9.675%   $21.606   $21.61   $21.60   $21.60  
  Purchase #5 $205.47   13.732%   $233.6851   $233.69   $233.70   $233.70  
  Purchase #6 $49.95   5.274%   $52.5844   $52.58   $52.60   $52.60  
  Purchase #7 $217.84   8.246%   $235.8031   $235.80   $235.80   $235.80  
  7 purchase totals = $632.98       $696.4408   $696.45   $696.45   $696.50