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 $29.82   7.451%   $32.0419   $32.04   $32.05   $32.00  
  Purchase #2 $73.28   12.721%   $82.6019   $82.60   $82.60   $82.60  
  Purchase #3 $98.50   3.176%   $101.6284   $101.63   $101.65   $101.60  
  Purchase #4 $196.56   12.338%   $220.8116   $220.81   $220.80   $220.80  
  Purchase #5 $207.99   7.242%   $223.0526   $223.05   $223.05   $223.10  
  Purchase #6 $130.54   9.797%   $143.329   $143.33   $143.35   $143.30  
  Purchase #7 $235.70   7.115%   $252.4701   $252.47   $252.45   $252.50  
  7 purchase totals = $972.39       $1,055.9355   $1,055.93   $1,055.95   $1,055.90