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 $49.43   8.490%   $53.6266   $53.63   $53.65   $53.60  
  Purchase #2 $164.82   13.670%   $187.3509   $187.35   $187.35   $187.40  
  Purchase #3 $137.53   7.779%   $148.2285   $148.23   $148.25   $148.20  
  Purchase #4 $14.87   13.808%   $16.9232   $16.92   $16.90   $16.90  
  Purchase #5 $101.67   7.500%   $109.2953   $109.30   $109.30   $109.30  
  Purchase #6 $81.41   6.826%   $86.967   $86.97   $86.95   $87.00  
  Purchase #7 $153.31   6.164%   $162.76   $162.76   $162.75   $162.80  
  7 purchase totals = $703.04       $765.1515   $765.16   $765.15   $765.20