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 $76.30   12.404%   $85.7643   $85.76   $85.75   $85.80  
  Purchase #2 $23.99   4.575%   $25.0875   $25.09   $25.10   $25.10  
  Purchase #3 $101.41   12.549%   $114.1359   $114.14   $114.15   $114.10  
  Purchase #4 $241.77   11.355%   $269.223   $269.22   $269.20   $269.20  
  Purchase #5 $243.50   13.103%   $275.4058   $275.41   $275.40   $275.40  
  Purchase #6 $88.25   8.320%   $95.5924   $95.59   $95.60   $95.60  
  Purchase #7 $223.28   11.517%   $248.9952   $249.00   $249.00   $249.00  
  7 purchase totals = $998.50       $1,114.2041   $1,114.21   $1,114.20   $1,114.20