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 $182.45   11.543%   $203.5102   $203.51   $203.50   $203.50  
  Purchase #2 $146.99   6.851%   $157.0603   $157.06   $157.05   $157.10  
  Purchase #3 $108.75   13.662%   $123.6074   $123.61   $123.60   $123.60  
  Purchase #4 $94.31   4.551%   $98.602   $98.60   $98.60   $98.60  
  Purchase #5 $187.87   8.410%   $203.6699   $203.67   $203.65   $203.70  
  Purchase #6 $200.38   3.324%   $207.0406   $207.04   $207.05   $207.00  
  Purchase #7 $239.38   9.539%   $262.2145   $262.21   $262.20   $262.20  
  7 purchase totals = $1,160.13       $1,255.7049   $1,255.70   $1,255.65   $1,255.70