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 $224.80   6.656%   $239.7627   $239.76   $239.75   $239.80  
  Purchase #2 $49.52   3.540%   $51.273   $51.27   $51.25   $51.30  
  Purchase #3 $176.89   4.295%   $184.4874   $184.49   $184.50   $184.50  
  Purchase #4 $72.53   12.681%   $81.7275   $81.73   $81.75   $81.70  
  Purchase #5 $127.78   5.301%   $134.5536   $134.55   $134.55   $134.60  
  Purchase #6 $207.54   11.615%   $231.6458   $231.65   $231.65   $231.60  
  Purchase #7 $137.90   9.522%   $151.0308   $151.03   $151.05   $151.00  
  7 purchase totals = $996.96       $1,074.4808   $1,074.48   $1,074.50   $1,074.50