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 $218.42   6.818%   $233.3119   $233.31   $233.30   $233.30  
  Purchase #2 $148.54   4.507%   $155.2347   $155.23   $155.25   $155.20  
  Purchase #3 $227.39   5.397%   $239.6622   $239.66   $239.65   $239.70  
  Purchase #4 $63.60   7.563%   $68.4101   $68.41   $68.40   $68.40  
  Purchase #5 $119.60   13.767%   $136.0653   $136.07   $136.05   $136.10  
  Purchase #6 $163.39   8.134%   $176.6801   $176.68   $176.70   $176.70  
  Purchase #7 $240.39   4.484%   $251.1691   $251.17   $251.15   $251.20  
  7 purchase totals = $1,181.33       $1,260.5334   $1,260.53   $1,260.50   $1,260.60