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 $149.63   12.116%   $167.7592   $167.76   $167.75   $167.80  
  Purchase #2 $205.49   10.548%   $227.1651   $227.17   $227.15   $227.20  
  Purchase #3 $110.32   4.447%   $115.2259   $115.23   $115.25   $115.20  
  Purchase #4 $191.74   3.492%   $198.4356   $198.44   $198.45   $198.40  
  Purchase #5 $54.40   6.733%   $58.0628   $58.06   $58.05   $58.10  
  Purchase #6 $23.71   11.392%   $26.411   $26.41   $26.40   $26.40  
  Purchase #7 $12.25   11.585%   $13.6692   $13.67   $13.65   $13.70  
  7 purchase totals = $747.54       $806.7288   $806.74   $806.70   $806.80