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 $32.48   12.197%   $36.4416   $36.44   $36.45   $36.40  
  Purchase #2 $70.81   13.704%   $80.5138   $80.51   $80.50   $80.50  
  Purchase #3 $208.43   6.356%   $221.6778   $221.68   $221.70   $221.70  
  Purchase #4 $60.61   6.567%   $64.5903   $64.59   $64.60   $64.60  
  Purchase #5 $114.79   4.174%   $119.5813   $119.58   $119.60   $119.60  
  Purchase #6 $212.93   10.542%   $235.3771   $235.38   $235.40   $235.40  
  Purchase #7 $244.50   8.812%   $266.0453   $266.05   $266.05   $266.00  
  7 purchase totals = $944.55       $1,024.2272   $1,024.23   $1,024.30   $1,024.20