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 $248.83   13.187%   $281.6432   $281.64   $281.65   $281.60  
  Purchase #2 $12.31   3.153%   $12.6981   $12.70   $12.70   $12.70  
  Purchase #3 $130.95   3.387%   $135.3853   $135.39   $135.40   $135.40  
  Purchase #4 $68.78   12.227%   $77.1897   $77.19   $77.20   $77.20  
  Purchase #5 $87.90   11.413%   $97.932   $97.93   $97.95   $97.90  
  Purchase #6 $164.60   8.411%   $178.4445   $178.44   $178.45   $178.40  
  Purchase #7 $208.99   13.212%   $236.6018   $236.60   $236.60   $236.60  
  7 purchase totals = $922.36       $1,019.8946   $1,019.89   $1,019.95   $1,019.80