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 $208.83   10.126%   $229.9761   $229.98   $230.00   $230.00  
  Purchase #2 $176.68   11.186%   $196.4434   $196.44   $196.45   $196.40  
  Purchase #3 $154.84   3.332%   $159.9993   $160.00   $160.00   $160.00  
  Purchase #4 $114.58   3.696%   $118.8149   $118.81   $118.80   $118.80  
  Purchase #5 $60.78   12.244%   $68.2219   $68.22   $68.20   $68.20  
  Purchase #6 $130.68   8.490%   $141.7747   $141.77   $141.75   $141.80  
  Purchase #7 $151.61   6.493%   $161.454   $161.45   $161.45   $161.50  
  7 purchase totals = $998.00       $1,076.6843   $1,076.67   $1,076.65   $1,076.70