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 $49.90   13.622%   $56.6974   $56.70   $56.70   $56.70  
  Purchase #2 $207.87   11.355%   $231.4736   $231.47   $231.45   $231.50  
  Purchase #3 $16.56   5.836%   $17.5264   $17.53   $17.55   $17.50  
  Purchase #4 $212.45   5.455%   $224.0391   $224.04   $224.05   $224.00  
  Purchase #5 $65.94   4.258%   $68.7477   $68.75   $68.75   $68.70  
  Purchase #6 $127.93   9.730%   $140.3776   $140.38   $140.40   $140.40  
  Purchase #7 $166.91   3.573%   $172.8737   $172.87   $172.85   $172.90  
  7 purchase totals = $847.56       $911.7355   $911.74   $911.75   $911.70