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 $210.93   10.116%   $232.2677   $232.27   $232.25   $232.30  
  Purchase #2 $222.81   12.538%   $250.7459   $250.75   $250.75   $250.70  
  Purchase #3 $186.81   11.748%   $208.7564   $208.76   $208.75   $208.80  
  Purchase #4 $91.73   8.129%   $99.1867   $99.19   $99.20   $99.20  
  Purchase #5 $130.44   4.628%   $136.4768   $136.48   $136.50   $136.50  
  Purchase #6 $134.43   10.176%   $148.1096   $148.11   $148.10   $148.10  
  Purchase #7 $148.32   9.228%   $162.007   $162.01   $162.00   $162.00  
  7 purchase totals = $1,125.47       $1,237.5501   $1,237.57   $1,237.55   $1,237.60