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 $86.60   12.864%   $97.7402   $97.74   $97.75   $97.70  
  Purchase #2 $38.95   4.247%   $40.6042   $40.60   $40.60   $40.60  
  Purchase #3 $70.65   3.473%   $73.1037   $73.10   $73.10   $73.10  
  Purchase #4 $86.81   10.180%   $95.6473   $95.65   $95.65   $95.60  
  Purchase #5 $24.51   11.415%   $27.3078   $27.31   $27.30   $27.30  
  Purchase #6 $83.44   12.122%   $93.5546   $93.55   $93.55   $93.60  
  Purchase #7 $114.65   7.113%   $122.8051   $122.81   $122.80   $122.80  
  7 purchase totals = $505.61       $550.7629   $550.76   $550.75   $550.70