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 $189.93   8.521%   $206.1139   $206.11   $206.10   $206.10  
  Purchase #2 $208.92   8.491%   $226.6594   $226.66   $226.65   $226.70  
  Purchase #3 $36.45   7.513%   $39.1885   $39.19   $39.20   $39.20  
  Purchase #4 $6.27   4.647%   $6.5614   $6.56   $6.55   $6.60  
  Purchase #5 $154.68   5.854%   $163.735   $163.74   $163.75   $163.70  
  Purchase #6 $45.76   11.188%   $50.8796   $50.88   $50.90   $50.90  
  Purchase #7 $192.94   6.593%   $205.6605   $205.66   $205.65   $205.70  
  7 purchase totals = $834.95       $898.7983   $898.80   $898.80   $898.90