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 $95.42   11.701%   $106.5851   $106.59   $106.60   $106.60  
  Purchase #2 $163.77   9.145%   $178.7468   $178.75   $178.75   $178.70  
  Purchase #3 $229.83   12.274%   $258.0393   $258.04   $258.05   $258.00  
  Purchase #4 $35.28   11.625%   $39.3813   $39.38   $39.40   $39.40  
  Purchase #5 $86.71   10.340%   $95.6758   $95.68   $95.70   $95.70  
  Purchase #6 $176.91   3.309%   $182.764   $182.76   $182.75   $182.80  
  Purchase #7 $195.36   11.262%   $217.3614   $217.36   $217.35   $217.40  
  7 purchase totals = $983.28       $1,078.5537   $1,078.56   $1,078.60   $1,078.60