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 $242.96   6.807%   $259.4983   $259.50   $259.50   $259.50  
  Purchase #2 $245.49   13.611%   $278.9036   $278.90   $278.90   $278.90  
  Purchase #3 $210.50   4.661%   $220.3114   $220.31   $220.30   $220.30  
  Purchase #4 $236.83   3.294%   $244.6312   $244.63   $244.65   $244.60  
  Purchase #5 $222.45   11.395%   $247.7982   $247.80   $247.80   $247.80  
  Purchase #6 $185.55   10.803%   $205.595   $205.60   $205.60   $205.60  
  Purchase #7 $55.41   13.432%   $62.8527   $62.85   $62.85   $62.90  
  7 purchase totals = $1,399.19       $1,519.5904   $1,519.59   $1,519.60   $1,519.60