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 $248.35   3.466%   $256.9578   $256.96   $256.95   $257.00  
  Purchase #2 $191.88   6.443%   $204.2428   $204.24   $204.25   $204.20  
  Purchase #3 $85.49   10.303%   $94.298   $94.30   $94.30   $94.30  
  Purchase #4 $155.76   7.255%   $167.0604   $167.06   $167.05   $167.10  
  Purchase #5 $126.85   9.268%   $138.6065   $138.61   $138.60   $138.60  
  Purchase #6 $116.45   6.566%   $124.0961   $124.10   $124.10   $124.10  
  Purchase #7 $168.45   5.799%   $178.2184   $178.22   $178.20   $178.20  
  7 purchase totals = $1,093.23       $1,163.4800   $1,163.49   $1,163.45   $1,163.50