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 $221.26   9.221%   $241.6624   $241.66   $241.65   $241.70  
  Purchase #2 $87.88   10.778%   $97.3517   $97.35   $97.35   $97.40  
  Purchase #3 $21.32   7.609%   $22.9422   $22.94   $22.95   $22.90  
  Purchase #4 $48.91   5.857%   $51.7747   $51.77   $51.75   $51.80  
  Purchase #5 $13.92   9.407%   $15.2295   $15.23   $15.25   $15.20  
  Purchase #6 $232.33   10.366%   $256.4133   $256.41   $256.40   $256.40  
  Purchase #7 $42.71   12.636%   $48.1068   $48.11   $48.10   $48.10  
  7 purchase totals = $668.33       $733.4806   $733.47   $733.45   $733.50