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 $242.89   8.108%   $262.5835   $262.58   $262.60   $262.60  
  Purchase #2 $212.65   12.593%   $239.429   $239.43   $239.45   $239.40  
  Purchase #3 $92.83   9.390%   $101.5467   $101.55   $101.55   $101.50  
  Purchase #4 $153.87   12.851%   $173.6438   $173.64   $173.65   $173.60  
  Purchase #5 $233.58   13.380%   $264.833   $264.83   $264.85   $264.80  
  Purchase #6 $145.63   4.797%   $152.6159   $152.62   $152.60   $152.60  
  Purchase #7 $230.32   12.757%   $259.7019   $259.70   $259.70   $259.70  
  7 purchase totals = $1,311.77       $1,454.3538   $1,454.35   $1,454.40   $1,454.20