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 $208.47   7.834%   $224.8015   $224.80   $224.80   $224.80  
  Purchase #2 $182.76   12.106%   $204.8849   $204.88   $204.90   $204.90  
  Purchase #3 $130.75   5.119%   $137.4431   $137.44   $137.45   $137.40  
  Purchase #4 $63.78   8.593%   $69.2606   $69.26   $69.25   $69.30  
  Purchase #5 $22.75   7.607%   $24.4806   $24.48   $24.50   $24.50  
  Purchase #6 $114.77   3.687%   $119.0016   $119.00   $119.00   $119.00  
  Purchase #7 $124.88   5.104%   $131.2539   $131.25   $131.25   $131.30  
  7 purchase totals = $848.16       $911.1262   $911.11   $911.15   $911.20