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 $119.69   4.168%   $124.6787   $124.68   $124.70   $124.70  
  Purchase #2 $60.68   10.220%   $66.8815   $66.88   $66.90   $66.90  
  Purchase #3 $91.48   3.537%   $94.7156   $94.72   $94.70   $94.70  
  Purchase #4 $137.26   11.240%   $152.688   $152.69   $152.70   $152.70  
  Purchase #5 $161.81   11.785%   $180.8793   $180.88   $180.90   $180.90  
  Purchase #6 $159.73   5.324%   $168.234   $168.23   $168.25   $168.20  
  Purchase #7 $188.26   9.285%   $205.7399   $205.74   $205.75   $205.70  
  7 purchase totals = $918.91       $993.8170   $993.82   $993.90   $993.80