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 $112.89   12.302%   $126.7777   $126.78   $126.80   $126.80  
  Purchase #2 $100.85   8.402%   $109.3234   $109.32   $109.30   $109.30  
  Purchase #3 $33.74   3.109%   $34.789   $34.79   $34.80   $34.80  
  Purchase #4 $247.88   5.477%   $261.4564   $261.46   $261.45   $261.50  
  Purchase #5 $207.92   8.495%   $225.5828   $225.58   $225.60   $225.60  
  Purchase #6 $148.58   4.296%   $154.963   $154.96   $154.95   $155.00  
  Purchase #7 $139.71   10.248%   $154.0275   $154.03   $154.05   $154.00  
  7 purchase totals = $991.57       $1,066.9198   $1,066.92   $1,066.95   $1,067.00