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 $249.34   4.761%   $261.2111   $261.21   $261.20   $261.20  
  Purchase #2 $105.63   3.536%   $109.3651   $109.37   $109.35   $109.40  
  Purchase #3 $76.41   5.276%   $80.4414   $80.44   $80.45   $80.40  
  Purchase #4 $21.44   11.147%   $23.8299   $23.83   $23.85   $23.80  
  Purchase #5 $195.30   6.799%   $208.5784   $208.58   $208.60   $208.60  
  Purchase #6 $195.96   12.155%   $219.7789   $219.78   $219.80   $219.80  
  Purchase #7 $202.88   4.622%   $212.2571   $212.26   $212.25   $212.30  
  7 purchase totals = $1,046.96       $1,115.4619   $1,115.47   $1,115.50   $1,115.50