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 $93.39   5.284%   $98.3247   $98.32   $98.30   $98.30  
  Purchase #2 $152.55   10.746%   $168.943   $168.94   $168.95   $168.90  
  Purchase #3 $8.85   7.103%   $9.4786   $9.48   $9.50   $9.50  
  Purchase #4 $179.63   3.451%   $185.829   $185.83   $185.85   $185.80  
  Purchase #5 $170.70   13.540%   $193.8128   $193.81   $193.80   $193.80  
  Purchase #6 $248.96   5.119%   $261.7043   $261.70   $261.70   $261.70  
  Purchase #7 $148.96   13.443%   $168.9847   $168.98   $169.00   $169.00  
  7 purchase totals = $1,003.04       $1,087.0771   $1,087.06   $1,087.10   $1,087.00