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 $179.87   12.628%   $202.584   $202.58   $202.60   $202.60  
  Purchase #2 $234.73   11.613%   $261.9892   $261.99   $262.00   $262.00  
  Purchase #3 $250.38   5.621%   $264.4539   $264.45   $264.45   $264.50  
  Purchase #4 $121.54   4.763%   $127.329   $127.33   $127.35   $127.30  
  Purchase #5 $71.65   13.826%   $81.5563   $81.56   $81.55   $81.60  
  Purchase #6 $232.43   11.707%   $259.6406   $259.64   $259.65   $259.60  
  Purchase #7 $18.64   3.375%   $19.2691   $19.27   $19.25   $19.30  
  7 purchase totals = $1,109.24       $1,216.8221   $1,216.82   $1,216.85   $1,216.90