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 $224.81   13.561%   $255.2965   $255.30   $255.30   $255.30  
  Purchase #2 $241.94   8.498%   $262.5001   $262.50   $262.50   $262.50  
  Purchase #3 $41.25   10.520%   $45.5895   $45.59   $45.60   $45.60  
  Purchase #4 $207.68   12.587%   $233.8207   $233.82   $233.80   $233.80  
  Purchase #5 $210.76   13.397%   $238.9955   $239.00   $239.00   $239.00  
  Purchase #6 $240.99   7.688%   $259.5173   $259.52   $259.50   $259.50  
  Purchase #7 $165.98   9.873%   $182.3672   $182.37   $182.35   $182.40  
  7 purchase totals = $1,333.41       $1,478.0868   $1,478.10   $1,478.05   $1,478.10