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 $52.62   7.691%   $56.667   $56.67   $56.65   $56.70  
  Purchase #2 $76.88   5.229%   $80.9001   $80.90   $80.90   $80.90  
  Purchase #3 $78.37   10.181%   $86.3488   $86.35   $86.35   $86.30  
  Purchase #4 $143.69   7.750%   $154.826   $154.83   $154.85   $154.80  
  Purchase #5 $174.61   9.774%   $191.6764   $191.68   $191.70   $191.70  
  Purchase #6 $6.66   3.110%   $6.8671   $6.87   $6.85   $6.90  
  Purchase #7 $242.27   11.227%   $269.4697   $269.47   $269.45   $269.50  
  7 purchase totals = $775.10       $846.7551   $846.77   $846.75   $846.80