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 $208.43   13.681%   $236.9453   $236.95   $236.95   $236.90  
  Purchase #2 $203.56   10.156%   $224.2336   $224.23   $224.25   $224.20  
  Purchase #3 $239.52   13.675%   $272.2744   $272.27   $272.25   $272.30  
  Purchase #4 $65.89   9.634%   $72.2378   $72.24   $72.25   $72.20  
  Purchase #5 $250.70   12.357%   $281.679   $281.68   $281.70   $281.70  
  Purchase #6 $144.50   3.212%   $149.1413   $149.14   $149.15   $149.10  
  Purchase #7 $112.33   6.180%   $119.272   $119.27   $119.25   $119.30  
  7 purchase totals = $1,224.93       $1,355.7834   $1,355.78   $1,355.80   $1,355.70