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 $23.33   7.334%   $25.041   $25.04   $25.05   $25.00  
  Purchase #2 $187.57   11.251%   $208.6735   $208.67   $208.65   $208.70  
  Purchase #3 $65.84   11.730%   $73.563   $73.56   $73.55   $73.60  
  Purchase #4 $112.49   12.176%   $126.1868   $126.19   $126.20   $126.20  
  Purchase #5 $49.50   7.832%   $53.3768   $53.38   $53.40   $53.40  
  Purchase #6 $20.76   13.420%   $23.546   $23.55   $23.55   $23.50  
  Purchase #7 $98.50   11.853%   $110.1752   $110.18   $110.20   $110.20  
  7 purchase totals = $557.99       $620.5623   $620.57   $620.60   $620.60