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 $114.44   3.778%   $118.7635   $118.76   $118.75   $118.80  
  Purchase #2 $163.78   12.284%   $183.8987   $183.90   $183.90   $183.90  
  Purchase #3 $56.95   6.559%   $60.6854   $60.69   $60.70   $60.70  
  Purchase #4 $27.42   4.639%   $28.692   $28.69   $28.70   $28.70  
  Purchase #5 $76.63   5.328%   $80.7128   $80.71   $80.70   $80.70  
  Purchase #6 $115.86   7.390%   $124.4221   $124.42   $124.40   $124.40  
  Purchase #7 $222.94   13.483%   $252.999   $253.00   $253.00   $253.00  
  7 purchase totals = $778.02       $850.1735   $850.17   $850.15   $850.20