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 $14.88   8.847%   $16.1964   $16.20   $16.20   $16.20  
  Purchase #2 $249.93   5.147%   $262.7939   $262.79   $262.80   $262.80  
  Purchase #3 $230.32   8.563%   $250.0423   $250.04   $250.05   $250.00  
  Purchase #4 $10.69   3.782%   $11.0943   $11.09   $11.10   $11.10  
  Purchase #5 $183.32   11.491%   $204.3853   $204.39   $204.40   $204.40  
  Purchase #6 $180.37   5.487%   $190.2669   $190.27   $190.25   $190.30  
  Purchase #7 $61.93   12.224%   $69.5003   $69.50   $69.50   $69.50  
  7 purchase totals = $931.44       $1,004.2794   $1,004.28   $1,004.30   $1,004.30