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 $237.90   5.348%   $250.6229   $250.62   $250.60   $250.60  
  Purchase #2 $201.56   3.510%   $208.6348   $208.63   $208.65   $208.60  
  Purchase #3 $184.72   5.661%   $195.177   $195.18   $195.20   $195.20  
  Purchase #4 $43.89   13.774%   $49.9354   $49.94   $49.95   $49.90  
  Purchase #5 $155.28   7.143%   $166.3717   $166.37   $166.35   $166.40  
  Purchase #6 $164.52   6.261%   $174.8206   $174.82   $174.80   $174.80  
  Purchase #7 $217.45   10.235%   $239.706   $239.71   $239.70   $239.70  
  7 purchase totals = $1,205.32       $1,285.2684   $1,285.27   $1,285.25   $1,285.20