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 $69.41   10.341%   $76.5877   $76.59   $76.60   $76.60  
  Purchase #2 $31.47   3.283%   $32.5032   $32.50   $32.50   $32.50  
  Purchase #3 $39.65   7.330%   $42.5563   $42.56   $42.55   $42.60  
  Purchase #4 $197.70   4.145%   $205.8947   $205.89   $205.90   $205.90  
  Purchase #5 $245.57   6.560%   $261.6794   $261.68   $261.70   $261.70  
  Purchase #6 $22.31   8.675%   $24.2454   $24.25   $24.25   $24.20  
  Purchase #7 $153.98   10.462%   $170.0894   $170.09   $170.10   $170.10  
  7 purchase totals = $760.09       $813.5561   $813.56   $813.60   $813.60