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 $245.47   8.873%   $267.2506   $267.25   $267.25   $267.30  
  Purchase #2 $151.37   7.342%   $162.4836   $162.48   $162.50   $162.50  
  Purchase #3 $188.25   3.424%   $194.6957   $194.70   $194.70   $194.70  
  Purchase #4 $135.56   5.715%   $143.3073   $143.31   $143.30   $143.30  
  Purchase #5 $8.91   7.780%   $9.6032   $9.60   $9.60   $9.60  
  Purchase #6 $41.71   12.436%   $46.8971   $46.90   $46.90   $46.90  
  Purchase #7 $167.70   9.256%   $183.2223   $183.22   $183.20   $183.20  
  7 purchase totals = $938.97       $1,007.4598   $1,007.46   $1,007.45   $1,007.50