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 $192.91   4.713%   $202.0018   $202.00   $202.00   $202.00  
  Purchase #2 $107.57   6.597%   $114.6664   $114.67   $114.65   $114.70  
  Purchase #3 $133.38   11.511%   $148.7334   $148.73   $148.75   $148.70  
  Purchase #4 $231.69   11.424%   $258.1583   $258.16   $258.15   $258.20  
  Purchase #5 $30.39   13.657%   $34.5404   $34.54   $34.55   $34.50  
  Purchase #6 $75.47   13.874%   $85.9407   $85.94   $85.95   $85.90  
  Purchase #7 $196.49   13.680%   $223.3698   $223.37   $223.35   $223.40  
  7 purchase totals = $967.90       $1,067.4108   $1,067.41   $1,067.40   $1,067.40