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 $236.73   5.331%   $249.3501   $249.35   $249.35   $249.40  
  Purchase #2 $146.29   13.177%   $165.5666   $165.57   $165.55   $165.60  
  Purchase #3 $115.88   8.871%   $126.1597   $126.16   $126.15   $126.20  
  Purchase #4 $95.92   5.673%   $101.3615   $101.36   $101.35   $101.40  
  Purchase #5 $239.97   3.546%   $248.4793   $248.48   $248.50   $248.50  
  Purchase #6 $71.78   6.406%   $76.3782   $76.38   $76.40   $76.40  
  Purchase #7 $197.95   5.361%   $208.5621   $208.56   $208.55   $208.60  
  7 purchase totals = $1,104.52       $1,175.8575   $1,175.86   $1,175.85   $1,176.10