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 $222.98   11.667%   $248.9951   $249.00   $249.00   $249.00  
  Purchase #2 $224.96   10.305%   $248.1421   $248.14   $248.15   $248.10  
  Purchase #3 $56.38   12.527%   $63.4427   $63.44   $63.45   $63.40  
  Purchase #4 $66.40   6.729%   $70.8681   $70.87   $70.85   $70.90  
  Purchase #5 $112.37   6.340%   $119.4943   $119.49   $119.50   $119.50  
  Purchase #6 $240.47   9.798%   $264.0313   $264.03   $264.05   $264.00  
  Purchase #7 $83.58   10.817%   $92.6208   $92.62   $92.60   $92.60  
  7 purchase totals = $1,007.14       $1,107.5944   $1,107.59   $1,107.60   $1,107.50