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 $6.25   5.752%   $6.6095   $6.61   $6.60   $6.60  
  Purchase #2 $224.62   3.478%   $232.4323   $232.43   $232.45   $232.40  
  Purchase #3 $161.39   13.178%   $182.658   $182.66   $182.65   $182.70  
  Purchase #4 $84.29   12.320%   $94.6745   $94.67   $94.65   $94.70  
  Purchase #5 $177.45   7.217%   $190.2566   $190.26   $190.25   $190.30  
  Purchase #6 $157.91   3.793%   $163.8995   $163.90   $163.90   $163.90  
  Purchase #7 $23.74   10.709%   $26.2823   $26.28   $26.30   $26.30  
  7 purchase totals = $835.65       $896.8127   $896.81   $896.80   $896.90