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 $91.38   6.136%   $96.9871   $96.99   $97.00   $97.00  
  Purchase #2 $108.56   5.288%   $114.3007   $114.30   $114.30   $114.30  
  Purchase #3 $249.61   4.795%   $261.5788   $261.58   $261.60   $261.60  
  Purchase #4 $240.54   6.330%   $255.7662   $255.77   $255.75   $255.80  
  Purchase #5 $85.92   7.392%   $92.2712   $92.27   $92.25   $92.30  
  Purchase #6 $247.71   12.181%   $277.8836   $277.88   $277.90   $277.90  
  Purchase #7 $219.41   13.299%   $248.5893   $248.59   $248.60   $248.60  
  7 purchase totals = $1,243.13       $1,347.3769   $1,347.38   $1,347.40   $1,347.50