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 $46.82   6.523%   $49.8741   $49.87   $49.85   $49.90  
  Purchase #2 $101.41   12.672%   $114.2607   $114.26   $114.25   $114.30  
  Purchase #3 $40.63   9.410%   $44.4533   $44.45   $44.45   $44.50  
  Purchase #4 $13.87   5.342%   $14.6109   $14.61   $14.60   $14.60  
  Purchase #5 $208.85   3.522%   $216.2057   $216.21   $216.20   $216.20  
  Purchase #6 $124.33   6.476%   $132.3816   $132.38   $132.40   $132.40  
  Purchase #7 $167.44   10.287%   $184.6646   $184.66   $184.65   $184.70  
  7 purchase totals = $703.35       $756.4509   $756.44   $756.40   $756.60