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 $112.28   12.356%   $126.1533   $126.15   $126.15   $126.20  
  Purchase #2 $195.72   9.217%   $213.7595   $213.76   $213.75   $213.80  
  Purchase #3 $142.41   8.765%   $154.8922   $154.89   $154.90   $154.90  
  Purchase #4 $25.39   11.611%   $28.338   $28.34   $28.35   $28.30  
  Purchase #5 $183.91   13.519%   $208.7728   $208.77   $208.75   $208.80  
  Purchase #6 $131.82   7.615%   $141.8581   $141.86   $141.85   $141.90  
  Purchase #7 $106.69   7.842%   $115.0566   $115.06   $115.05   $115.10  
  7 purchase totals = $898.22       $988.8305   $988.83   $988.80   $989.00