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 $225.53   13.717%   $256.466   $256.47   $256.45   $256.50  
  Purchase #2 $194.92   9.621%   $213.6733   $213.67   $213.65   $213.70  
  Purchase #3 $164.53   8.830%   $179.058   $179.06   $179.05   $179.10  
  Purchase #4 $85.70   10.531%   $94.7251   $94.73   $94.75   $94.70  
  Purchase #5 $193.40   7.763%   $208.4136   $208.41   $208.40   $208.40  
  Purchase #6 $56.85   12.220%   $63.7971   $63.80   $63.80   $63.80  
  Purchase #7 $185.54   3.692%   $192.3901   $192.39   $192.40   $192.40  
  7 purchase totals = $1,106.47       $1,208.5232   $1,208.53   $1,208.50   $1,208.60