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 $86.80   13.512%   $98.5284   $98.53   $98.55   $98.50  
  Purchase #2 $8.55   11.118%   $9.5006   $9.50   $9.50   $9.50  
  Purchase #3 $161.64   4.300%   $168.5905   $168.59   $168.60   $168.60  
  Purchase #4 $197.91   12.262%   $222.1777   $222.18   $222.20   $222.20  
  Purchase #5 $78.93   9.234%   $86.2184   $86.22   $86.20   $86.20  
  Purchase #6 $168.51   13.680%   $191.5622   $191.56   $191.55   $191.60  
  Purchase #7 $68.51   7.662%   $73.7592   $73.76   $73.75   $73.80  
  7 purchase totals = $770.85       $850.3370   $850.34   $850.35   $850.40