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 $58.95   8.376%   $63.8877   $63.89   $63.90   $63.90  
  Purchase #2 $209.61   6.269%   $222.7505   $222.75   $222.75   $222.80  
  Purchase #3 $8.45   3.695%   $8.7622   $8.76   $8.75   $8.80  
  Purchase #4 $71.27   9.683%   $78.1711   $78.17   $78.15   $78.20  
  Purchase #5 $171.80   12.418%   $193.1341   $193.13   $193.15   $193.10  
  Purchase #6 $65.58   10.599%   $72.5308   $72.53   $72.55   $72.50  
  Purchase #7 $144.68   4.579%   $151.3049   $151.30   $151.30   $151.30  
  7 purchase totals = $730.34       $790.5413   $790.53   $790.55   $790.60