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 $113.76   11.469%   $126.8071   $126.81   $126.80   $126.80  
  Purchase #2 $94.89   3.759%   $98.4569   $98.46   $98.45   $98.50  
  Purchase #3 $8.47   11.336%   $9.4302   $9.43   $9.45   $9.40  
  Purchase #4 $227.32   11.602%   $253.6937   $253.69   $253.70   $253.70  
  Purchase #5 $155.82   3.654%   $161.5137   $161.51   $161.50   $161.50  
  Purchase #6 $106.40   11.350%   $118.4764   $118.48   $118.50   $118.50  
  Purchase #7 $249.30   4.320%   $260.0698   $260.07   $260.05   $260.10  
  7 purchase totals = $955.96       $1,028.4478   $1,028.45   $1,028.45   $1,028.50