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 $56.54   5.380%   $59.5819   $59.58   $59.60   $59.60  
  Purchase #2 $118.71   3.686%   $123.0857   $123.09   $123.10   $123.10  
  Purchase #3 $54.84   4.393%   $57.2491   $57.25   $57.25   $57.20  
  Purchase #4 $50.91   9.610%   $55.8025   $55.80   $55.80   $55.80  
  Purchase #5 $119.75   3.674%   $124.1496   $124.15   $124.15   $124.10  
  Purchase #6 $64.56   8.642%   $70.1393   $70.14   $70.15   $70.10  
  Purchase #7 $220.93   7.287%   $237.0292   $237.03   $237.05   $237.00  
  7 purchase totals = $686.24       $727.0373   $727.04   $727.10   $726.90