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 $246.55   7.650%   $265.4111   $265.41   $265.40   $265.40  
  Purchase #2 $229.42   5.103%   $241.1273   $241.13   $241.15   $241.10  
  Purchase #3 $241.44   12.347%   $271.2506   $271.25   $271.25   $271.30  
  Purchase #4 $55.84   3.520%   $57.8056   $57.81   $57.80   $57.80  
  Purchase #5 $116.36   8.207%   $125.9097   $125.91   $125.90   $125.90  
  Purchase #6 $114.63   10.287%   $126.422   $126.42   $126.40   $126.40  
  Purchase #7 $163.62   10.583%   $180.9359   $180.94   $180.95   $180.90  
  7 purchase totals = $1,167.86       $1,268.8622   $1,268.87   $1,268.85   $1,268.80