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 $64.90   5.669%   $68.5792   $68.58   $68.60   $68.60  
  Purchase #2 $223.97   13.172%   $253.4713   $253.47   $253.45   $253.50  
  Purchase #3 $187.87   12.253%   $210.8897   $210.89   $210.90   $210.90  
  Purchase #4 $248.99   12.677%   $280.5545   $280.55   $280.55   $280.60  
  Purchase #5 $143.57   13.752%   $163.3137   $163.31   $163.30   $163.30  
  Purchase #6 $241.76   7.523%   $259.9476   $259.95   $259.95   $259.90  
  Purchase #7 $154.65   5.723%   $163.5006   $163.50   $163.50   $163.50  
  7 purchase totals = $1,265.71       $1,400.2566   $1,400.25   $1,400.25   $1,400.30