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 $59.81   6.473%   $63.6815   $63.68   $63.70   $63.70  
  Purchase #2 $142.56   4.866%   $149.497   $149.50   $149.50   $149.50  
  Purchase #3 $124.82   8.655%   $135.6232   $135.62   $135.60   $135.60  
  Purchase #4 $81.90   7.190%   $87.7886   $87.79   $87.80   $87.80  
  Purchase #5 $28.95   6.867%   $30.938   $30.94   $30.95   $30.90  
  Purchase #6 $126.31   10.606%   $139.7064   $139.71   $139.70   $139.70  
  Purchase #7 $113.47   9.384%   $124.118   $124.12   $124.10   $124.10  
  7 purchase totals = $677.82       $731.3527   $731.36   $731.35   $731.30