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 $184.42   11.539%   $205.7002   $205.70   $205.70   $205.70  
  Purchase #2 $161.45   4.501%   $168.7169   $168.72   $168.70   $168.70  
  Purchase #3 $249.93   8.247%   $270.5417   $270.54   $270.55   $270.50  
  Purchase #4 $94.62   7.262%   $101.4913   $101.49   $101.50   $101.50  
  Purchase #5 $78.44   5.815%   $83.0013   $83.00   $83.00   $83.00  
  Purchase #6 $213.46   12.808%   $240.8   $240.80   $240.80   $240.80  
  Purchase #7 $186.61   3.697%   $193.509   $193.51   $193.50   $193.50  
  7 purchase totals = $1,168.93       $1,263.7604   $1,263.76   $1,263.75   $1,263.70