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 $104.80   13.429%   $118.8736   $118.87   $118.85   $118.90  
  Purchase #2 $168.93   10.614%   $186.8602   $186.86   $186.85   $186.90  
  Purchase #3 $71.91   7.756%   $77.4873   $77.49   $77.50   $77.50  
  Purchase #4 $61.66   7.236%   $66.1217   $66.12   $66.10   $66.10  
  Purchase #5 $195.57   3.575%   $202.5616   $202.56   $202.55   $202.60  
  Purchase #6 $41.94   3.670%   $43.4792   $43.48   $43.50   $43.50  
  Purchase #7 $238.69   4.105%   $248.4882   $248.49   $248.50   $248.50  
  7 purchase totals = $883.50       $943.8718   $943.87   $943.85   $944.00