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 $116.34   8.513%   $126.244   $126.24   $126.25   $126.20  
  Purchase #2 $155.51   11.200%   $172.9271   $172.93   $172.95   $172.90  
  Purchase #3 $16.48   12.193%   $18.4894   $18.49   $18.50   $18.50  
  Purchase #4 $97.72   5.309%   $102.908   $102.91   $102.90   $102.90  
  Purchase #5 $83.65   8.379%   $90.659   $90.66   $90.65   $90.70  
  Purchase #6 $221.34   7.188%   $237.2499   $237.25   $237.25   $237.20  
  Purchase #7 $72.44   5.874%   $76.6951   $76.70   $76.70   $76.70  
  7 purchase totals = $763.48       $825.1725   $825.18   $825.20   $825.10